U.S. patent application number 15/190479 was filed with the patent office on 2017-12-28 for device and method for containing and tracking a subject using satellite positioning data.
The applicant listed for this patent is OnPoint Systems, LLC, Sunrise Labs, Inc.. Invention is credited to John Elwell Mason, Xinnakone Vivathana.
Application Number | 20170374503 15/190479 |
Document ID | / |
Family ID | 60629186 |
Filed Date | 2017-12-28 |
United States Patent
Application |
20170374503 |
Kind Code |
A1 |
Mason; John Elwell ; et
al. |
December 28, 2017 |
Device and Method For Containing and Tracking A Subject Using
Satellite Positioning Data
Abstract
A device to be disposed on a subject for determining whether the
subject is inside or outside of a containment zone defined by a
containment perimeter. There is a positioning unit for generating
position data, including satellite positioning data, of the
subject; the position data. There is a processor unit, in
communication with the positioning unit, configured to receive data
from a memory representing a plurality of line segments forming the
containment perimeter and obtain the position data of the subject.
The processor casts a ray from the position of the subject toward a
line segment of the containment perimeter and determines the number
of line segments that are intersected by the ray. The processor
determines from number of line segments intersected by the ray, if
the subject is inside the containment zone or outside of the
containment zone.
Inventors: |
Mason; John Elwell;
(Hampton, NH) ; Vivathana; Xinnakone; (Stratham,
NH) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
OnPoint Systems, LLC
Sunrise Labs, Inc. |
Bedford
Auburn |
NH
NH |
US
US |
|
|
Family ID: |
60629186 |
Appl. No.: |
15/190479 |
Filed: |
June 23, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04W 4/021 20130101;
H04W 4/025 20130101 |
International
Class: |
H04W 4/02 20090101
H04W004/02 |
Claims
1. A device to be disposed on a subject for determining whether the
subject is inside or outside of a containment zone defined by a
containment perimeter, the device comprising: A positioning unit
for generating position data corresponding to the position of the
subject; the position data including satellite positioning data;
and A processor unit, in communication with the positioning unit,
configured to: Receive data from a memory representing a plurality
of line segments forming the containment perimeter; Obtain from the
positioning unit the position data corresponding to the position of
the subject; Mathematically cast a ray from the position of the
subject toward a line segment of the plurality of line segments
representing the containment perimeter; Mathematically determine
the number of line segments of the plurality of line segments that
are intersected by the ray; and Determine, from the number of line
segments of the plurality of line segments intersected by the ray,
whether the subject is inside the containment zone or outside of
the containment zone.
2. The device of claim 1 wherein if the number of line segments of
the plurality of line segments intersected by the ray is an odd
number the subject is determined to be inside the containment zone
and if the number of line segments of the plurality of line
segments intersected by the ray is an even number the subject is
determined to be outside of the containment zone.
3. The device of claim 1 wherein the line segment of the plurality
of line segments representing the containment perimeter toward
which the ray is cast is line segment closest to the position of
the subject.
4. The device of claim 1 wherein the positioning unit includes a
global navigation satellite system receiver in communication with a
plurality of satellite constellations to produce the satellite
positioning data and wherein the positioning unit further includes
an attitude and heading reference system configured to provide to
the processor unit attitude and reference data regarding the
subject; wherein the position data includes the attitude and
reference data.
5. The device of claim 4 wherein the attitude and heading reference
system comprises one or more of a gyroscope, accelerometer, and a
magnetometer.
6. The device of claim 1 further including a correction unit
configured to issue a stimulus to the subject when the subject is
determined to be outside of the containment zone; wherein the
correction unit includes a static circuit for issuing the stimulus
to the subject in the form of a static correction when the subject
exits the containment zone, and wherein the correction unit further
includes an audio speaker for issuing an audible correction when
the subject is within a predetermined distance of a perimeter of
the containment zone.
7. The device of claim 6 further including a communication unit, in
communication with the processor unit, configured to transmit an
alert to an electronic device of an operator by way of a
communication network when the subject exits the containment
zone.
8. The device of claim 1 wherein the subject is one of an animal, a
human, or an object.
9. The device of claim 1 wherein the device is in the form of a
collar.
10. A method for determining whether a subject wearing a device is
inside or outside of a containment zone defined by a containment
perimeter, the method comprising: Generating position data
corresponding to the position of the subject; the position data
including satellite positioning data; Receiving data from a memory
representing a plurality of line segments forming the containment
perimeter; Mathematically casting a ray from the position of the
subject toward a line segment of the plurality of line segments
representing the containment perimeter Mathematically determining
the number of line segments of the plurality of line segments that
are intersected by the ray; and Determining, from the number of
line segments of the plurality of line segments intersected by the
ray, whether the subject is inside the containment zone or outside
of the containment zone.
11. The method of claim 10 wherein the step of determining if the
subject is inside the containment zone or outside of the
containment zone includes determining if the number of line
segments of the plurality of line segments intersected by the ray
is an odd number in which case the subject is determined to be
inside the containment zone and determining if the number of line
segments of the plurality of line segments intersected by the ray
is an even number in which case the subject is determined to be
outside of the containment zone.
12. The method of claim 10 wherein the line segment of the
plurality of line segments representing the containment perimeter
toward which the ray is cast is line segment closest to the
position of the subject.
13. The method of claim 10 wherein the step of generating position
data includes using a global navigation satellite system receiver
in communication with a plurality of satellite constellations to
produce the satellite positioning data and wherein the step of
generating position data further includes using an attitude and
heading reference system configured to provide to the processor
unit attitude and reference data regarding the subject; wherein the
position data includes the attitude and reference data.
14. The method of claim 13 wherein the attitude and heading
reference system comprises one or more of a gyroscope,
accelerometer, and a magnetometer.
15. The method of claim 10 further including issuing a stimulus to
the subject when the subject is determined to be outside of the
containment zone; wherein the step of issuing a stimulus includes
using a static circuit for issuing the stimulus to the subject in
the form of a static correction when the subject exits the
containment zone, and wherein the step of issuing a stimulus
further includes using an audio speaker for issuing an audible
correction when the subject is within a predetermined distance of a
perimeter of the containment zone.
16. The method of claim 15 further including transmitting an alert
to an electronic device of an operator by way of a communication
network when the subject exits the containment zone.
17. The method of claim 10 wherein the subject is one of an animal,
a human, or an object.
18. The method of claim 10 wherein the device is in the form of a
collar.
Description
FIELD OF INVENTION
[0001] This invention relates to containing and tracking a subject,
e.g. an animal, a human, or an object such as a vehicle, using
satellite positioning data and more specifically to such a system
which uses additional data to augment the satellite positioning
data to improve positioning accuracy.
BACKGROUND
[0002] Containment systems for animals/pets, in particular dogs,
have been used for several decades. The most commonly used
containment system is the buried wire fence system, which uses a
stimulus collar worn by the pet and the containment area is defined
by a buried wire. When the pet approaches the buried wire the
collar picks up a radio signal. The radio signal is generated by a
control box, which is located inside the pet owner's residence and
sent through the buried wire. Typically, there is a warning zone
close to the boundary and when the pet reaches this zone the collar
emits an audible signal. If the pet continues to the boundary, the
collar will issue a static correction, hopefully causing the pet to
retreat to the containment area.
[0003] There are certain inherent deficiencies and limitations with
buried wire fence systems. Since these systems require a control
box located within the pet owner's home with an uninterrupted power
source and a length of wire buried in the ground, installation is
difficult and generally requires a professional, which is expensive
and time consuming. Additionally, once the installation is
complete, the system typically remains buried at the property in
the original configuration since removal and/or modification would
be very costly.
[0004] Another inherent issue is that the buried wires tend to
break in geographic regions that have changing seasons, due to
freezing and thawing. Broken wires result in failure of the system,
potentially allowing the pet to escape. This is particularly
problematic since buried wire systems are open loop systems, i.e.
they provide no feedback to the pet owner if the pet escapes.
[0005] With the limitations of buried wire systems, other animal
containment systems which operate wirelessly have been introduced
and provide some incremental improvements. These systems solve the
problems associated with burying wires in the ground, however they
still have a major limitation; namely, they are also open loop
systems and do not provide feedback to the owner in the event the
pet escapes the containment area.
[0006] Wireless systems have other limitations based on how they
operate. The general operating principle is that the base station
emits a radio signal and the collar detects the signal strength.
When a defined low signal level threshold is detected, the collar
will emit an audible correction and when it crosses an even lower
threshold, the collar will issue a static correction.
[0007] The base station projects the radio signal in all directions
equally, thus the containment area is always circular in shape. The
owner defines the circle size by adjusting a radius dial on the
base station, up to a maximum radius. Of course, yards take on
various shapes and sizes and with the system being limited to a
circular containment area it provides limited flexibility.
Additionally, the pet owner must be careful that the signal does
not project onto unwanted or undesired areas, such as neighboring
yards or, even worse, busy streets. For large yards, multiple base
stations may be needed and they must be set up in a fashion that
the radio signals overlap in order for the pet to have a common
coverage area and thus a pathway to roam between containment
areas.
[0008] A further limiting aspect of the wireless solution is that
the collar receives the radio signal from the base station via Line
of Sight (LoS). Because of this, the emitting circle may become
irregular in shape based on landscape effects and any object
between the base station and the collar. This known phenomenon
limits the styles and types of suitable yards to generally flat and
clear areas to maximize the full distance of the circle.
[0009] Also available on the market is a wireless pet containment
system using Global Positioning System (GPS). This system does not
require buried wire and does provide more flexibility and
customization regarding the containment area. It does however still
require a base station and professional installation. The method
used in this system is called a Real Time Kinematic (RTK) system,
which is comprised of a base and a rover (i.e. collar).
[0010] Common in GPS and other satellite systems are the inherent
positioning errors that come with the technology. GPS/other
satellite system receivers receive and lock onto multiple
satellites to determine location on earth. Because the satellites
are several thousands of kilometers away, the signals they emit are
subject to interference when traveling through earth's atmosphere
(ionospheric errors). When the signals reach earth's surface, even
more error is introduced by the local environment. Trees,
buildings, land, and other objects reflect GPS/other satellite
system signals and cause them to propagate differently. This causes
delays and polarization effects. Positioning errors of this type
are called multipath errors and play a significant role in the
overall GPS/other satellite system error budget.
[0011] With the RTK system, the base is stationary and can minimize
the overall positioning error by using carrier phase tracking.
Error corrections are then sent by the base station to the
rover/collar to reduce positional error of the collar. Thus, the
RTK system has a stationary reference point and collar reference
point and can actively track the distance of the rover from the
base station with a high degree of accuracy.
[0012] However, there are shortcomings with the RTK system. First,
the system requires a professional technician not only to install
it, but also to modify any collar or containment area settings
thereafter. Additionally, the distance from the base station (and
hence the size of the containment area) is limited by LoS and local
environmental obstructions. Moreover, the base needs an
unobstructed view of the sky as well as an uninterrupted power
source to work properly. And, as with the other systems described
above, the system is an open loop system and does not provide
feedback to the owner in the event the pet escapes the containment
area.
[0013] In addition to pet containment systems, there has been a
rise in pet collar tracking and location devices. Some location
devices use cellular technology, which is limited by coverage area
and is not very accurate. A preferred technology for tracking the
location of pets uses the Global Navigation Satellite System
(GNSS). Although, GNSS is not a perfect solution as there are many
sources of error that impact location accuracy. While some errors
are externally induced by the atmosphere and the local environment,
others are introduced by the quality and type of technology used to
build the GNSS receiver system.
[0014] One of the most critical aspects is the placement and type
of antenna used in the GNSS receiver system within the pet collar.
Current location and tracking collars are poorly architected and
designed using sub-par components and techniques to reduce GNSS
errors. Another important aspect is the GNSS receiver's inability
to filter out erroneous signals. Large and closely spaced buildings
in cities form so called "urban canyons" which cause significant
multipath errors that can be upwards of tens or even hundreds of
meters. Current tracking collars do not account for such
environments and can cause large inaccuracies that misguide pet
owners to their pets. In frantic moments, pet owners need accurate
technology and techniques to be able to find their pets as
efficiently as possible.
SUMMARY
[0015] It is therefore an object of the invention to provide a
system which not only is capable of containing a pet (or other
subject) to a defined area but which is also capable of accurately
tracking the location of the pet if it escapes the containment
area.
[0016] It is a further object of the invention to provide a
containment system which may be easily installed and moved or
reconfigured to provide a different containment area.
[0017] In one aspect, the invention features a device to be
disposed on a subject for determining whether the subject is inside
or outside of a containment zone defined by a containment
perimeter. There is a positioning unit for generating position data
corresponding to the position of the subject; the position data
including satellite positioning data. There is a processor unit, in
communication with the positioning unit, configured to receive data
from a memory representing a plurality of line segments forming the
containment perimeter and obtain from the positioning unit the
position data corresponding to the position of the subject. The
processor casts a ray from the position of the subject toward a
line segment of the plurality of line segments representing the
containment perimeter determines the number of line segments of the
plurality of line segments that are intersected by the ray. The
processor unit then determines from number of line segments of the
plurality of line segments intersected by the ray if the subject is
inside the containment zone or outside of the containment zone.
[0018] In other aspects of the invention one or more of the
following features may be included. The number of line segments of
the plurality of line segments intersected by the ray is an odd
number the subject may be determined to be inside the containment
zone and if the number of line segments of the plurality of line
segments intersected by the ray is an even number the subject may
be determined to be outside of the containment zone. The line
segment of the plurality of line segments representing the
containment perimeter toward which the ray is cast may be line
segment closest to the position of the subject. The positioning
unit may include a global navigation satellite system receiver in
communication with a plurality of satellite constellations to
produce the satellite positioning data and wherein the positioning
unit may further include an attitude and heading reference system
configured to provide to the processor unit attitude and reference
data regarding the subject; wherein the position data includes the
attitude and reference data. The attitude and heading reference
system may comprise one or more of a gyroscope, accelerometer, and
a magnetometer. The device may further include a correction unit
configured to issue a stimulus to the subject when the subject is
determined to be outside of the containment zone; wherein the
correction unit includes a static circuit for issuing the stimulus
to the subject in the form of a static correction when the subject
exits the containment zone, and wherein the correction unit further
includes an audio speaker for issuing an audible correction when
the subject is within a predetermined distance of a perimeter of
the containment zone. The device may further include a
communication unit, in communication with the processor unit,
configured to transmit an alert to an electronic device of an
operator by way of a communication network when the subject exits
the containment zone. The subject may be one of an animal, a human,
or an object. The device may be in the form of a collar.
[0019] In another aspect, the invention features a method for
determining whether a subject wearing a device is inside or outside
of a containment zone defined by a containment perimeter. The
method includes generating position data corresponding to the
position of the subject; the position data including satellite
positioning data and receiving data from a memory representing a
plurality of line segments forming the containment perimeter. The
method also includes casting a ray from the position of the subject
toward a line segment of the plurality of line segments
representing the containment perimeter and determining the number
of line segments of the plurality of line segments that are
intersected by the ray. The method additionally includes
determining from number of line segments of the plurality of line
segments intersected by the ray if the subject is inside the
containment zone or outside of the containment zone.
[0020] In further aspects of the invention one or more of the
following features may be included. The step of determining if the
subject is inside the containment zone or outside of the
containment zone may include determining if the number of line
segments of the plurality of line segments intersected by the ray
is an odd number in which case the subject is determined to be
inside the containment zone and determining if the number of line
segments of the plurality of line segments intersected by the ray
is an even number in which case the subject is determined to be
outside of the containment zone. The line segment of the plurality
of line segments representing the containment perimeter toward
which the ray is cast may be the line segment closest to the
position of the subject. The step of generating position data may
include using a global navigation satellite system receiver in
communication with a plurality of satellite constellations to
produce the satellite positioning data and wherein the step of
generating position data further includes using an attitude and
heading reference system configured to provide to the processor
unit attitude and reference data regarding the subject; wherein the
position data includes the attitude and reference data. The
attitude and heading reference system may comprise one or more of a
gyroscope, accelerometer, and a magnetometer. The method may
further include issuing a stimulus to the subject when the subject
is determined to be outside of the containment zone; wherein the
step of issuing a stimulus includes using a static circuit for
issuing the stimulus to the subject in the form of a static
correction when the subject exits the containment zone, and wherein
step of issuing a stimulus further includes using an audio speaker
for issuing an audible correction when the subject is within a
predetermined distance of a perimeter of the containment zone. The
method may further include transmitting an alert to an electronic
device of an operator by way of a communication network when the
subject exits the containment zone. The subject may be one of an
animal, a human, or an object. The device may be in the form of a
collar.
[0021] These and other features of the invention will be apparent
from the following detailed description and the accompanying
figures, in which:
BRIEF DESCRIPTION OF THE FIGURES
[0022] FIG. 1 is a map of a containment area established according
to the invention;
[0023] FIG. 2 is a perspective view of a stimulus collar according
to the invention;
[0024] FIG. 3 is a schematic block diagram of the electronic
components of the stimulus collar of FIG. 2;
[0025] FIG. 4 is a state diagram depicting the top level software
states for the stimulus collar;
[0026] FIG. 5 is a state diagram depicting the software states for
the run state of FIG. 4;
[0027] FIG. 6 is state diagram depicting the software sub-states
for the containment state
[0028] FIG. 7 is flow diagram depicting the learn mode of FIG.
5;
[0029] FIG. 8A is flow diagram depicting the record way point step
of the flow diagram of FIG. 7;
[0030] FIG. 8B is a block diagram depicting the linearization step
of the flow diagram of FIG. 8A;
[0031] FIG. 9 is flow diagram depicting method of assessing the
validity of a containment perimeter;
[0032] FIG. 10 is a diagram depicting the impact of possible GNSS
system errors in establishing a containment perimeter;
[0033] FIG. 11 is a diagram depicting the saw tooth correction
method for reducing the impact of possible GNSS system errors shown
in FIG. 10;
[0034] FIG. 12A is a diagrammatic representation of a containment
zone in the shape of a polygon;
[0035] FIG. 12B is a diagrammatic representation of a containment
zone in the shape of a polygon depicting a ray intersecting the
plane of the polygon;
[0036] FIG. 13 is a diagram depicting a containment area and
application of the ray casting according to this invention;
[0037] FIG. 14 is a flow chart depicting the method of correcting
GNSS walking errors; and
[0038] FIG. 15 is a top plan view of a containment area
incorporating a structure.
DETAILED DESCRIPTION
[0039] To assist understanding of the invention, a preferred
embodiment will be described in detail below. The detailed
description of the preferred embodiment of the invention will be
directed to a pet containment and tracking system and method, but
the invention is also capable of use with other types of subjects,
including farm animals and even people. With respect to people,
useful applications include containing and tracking children, the
elderly, as well as individuals who are under house arrest or the
like. Of course, with people, the system would not use the typical
static correction used with pets/animals. The invention may also be
extended to containing and tracking mobile objects, such as
bicycles, automobiles, motorcycles and the like.
[0040] Referring to FIG. 1, once a containment area 10 is
established and activated, as described in detail below, the system
will operate in a containment mode and utilize a subset of
algorithms and augmented GNSS positioning information to track the
pet and keep it within the containment area, which includes safe
zone 12 and warning zone 14. Any area outside of containment area
10 is considered to be in out of bounds zone 16.
[0041] When the pet is in safe zone 12, as indicated at location
18, a collar, such as stimulus collar 30, FIG. 2, worn by the pet
will operate with no audible or static corrections issued. However,
as the pet moves toward and crosses the perimeter 20 defining
warning zone 14, to position 22, the collar 30 will issue an
audible correction until the pet moves back into safe zone 12. The
perimeter 20 of warning zone 14 may be established by offsetting it
a predetermined distance (in this example it is 3 meters, but could
be any suitable distance) from the containment perimeter 24 of
containment area 10. If instead of retreating to safe zone 12 when
hearing the audible warning, the pet continues through warning zone
14 and breaches containment perimeter 24, to position 26, for
example, the system determines that the pet is in out of bounds
zone 16 and issues a static correction.
[0042] Stimulus collar 30 will issue a static correction only for a
predetermined maximum time while the pet is in out of bounds zone
16. Once this predetermined time has elapsed, the collar 30 will
transition into a tracking mode and issue an alert to a cloud
server and subsequently update the pet owner's smart device
advising that the pet has escaped containment area 10. As long as
the pet is in out of bounds zone 16, collar 30 will issue continual
updates to the cloud server and subsequently update the pet owner's
smart device with location information. From the cloud server or
the pet owner's smart device, additional information, for example,
the pet's name, pet's location, bread crumb trail of the pet,
whether the pet is moving or not moving, distance from the
containment area 10, distance from the smart device to the pet,
time the pet left the containment area and the directions to the
pet's then current location may be provided.
[0043] If the pet is in the out of bounds zone 16 and re-enters the
containment area 10 the collar will not issue another static
correction and the pet will be allowed to safely re-enter the
containment area 10 and the collar will re-enter the containment
mode of operation. Another alert will be sent to the pet owner's
smart device stating that the pet has safely returned to
containment area 10.
[0044] Shown in FIG. 2, is a particular design of stimulus collar
30 which includes a user interface 32 with a display 34, such as an
LED or OLED display, and buttons 36 for the user to input
information. Collar 30 includes a band 38 which may be secured by a
clasp 40 comfortably around the neck of the pet. Clasp 40 may be
any suitable type of clasp, including one which mechanically
engages the ends of the band 38. The invention is not limited to
use in the form of a collar for a pet. Any suitable means for
securing a device for providing containment and tracking according
to this invention may be affixed to animals, humans or mobile
objects such as bicycles, automobiles, motorcycles and the like.
Although not shown in this figure, a speaker for issuing audible
corrections and probes for contacting the pet for issuing static
corrections would be included on collar 30.
[0045] The electronic components/peripherals of stimulus collar 30
are shown in schematic block diagram 50, FIG. 3. This includes
processing unit 52 which is in communication with user interface
unit 54, communication unit 56, static/audible correction unit 58
and precision positioning unit 60. Processing unit 52 includes
microprocessor 70 to provide overall control for the electronics
and functionality of the stimulus collar 30 and a memory 72, which
stores software to execute the functionality of the collar 30 as
well as store the maps of containment areas defined by the
user.
[0046] User interface 54 includes buttons 74 for the user to input
information and/or select options and functions presented on OLED
display 76. The information is provided to the processing unit 52
to be acted upon and the processing unit provides display
information to the OLED display 76 to be viewed by the user.
[0047] The communication unit 56 includes a cellular communications
device 80, which may further comprise a 2G cellular--Global System
for mobile Communication (GSM)/General Packet Radio Service (GPRS)
and 3G cellular--Universal Mobile Telecommunications System
(UMTS)/High Speed Packet Access (HSPA). The cellular communications
device 80 is used to complete the closed loop system of this
invention by providing critical alerts and information to the pet
owner. When the pet has escaped the containment area the system
switches to the tracking mode and provides information to the pet
owner, such as pet location and other information, as described
above. It can also provide other useful information such as battery
status information or system error messages.
[0048] Communication unit 56 additionally includes a Bluetooth Low
Energy (BLE) module 78 for communication with a fob (or,
alternatively, the pet owner's smart device), which the operator
may use during training of the pet to issue corrections. The
fob/smart device transmits signals which are received by the BLE
module 78 and the BLE Module 78 communicates with the
static/audible correction unit 58 (through processor unit 52) to
issue audible corrections via speaker unit 82 and static
corrections via static circuit 84 for containment and behavioral
reinforcements.
[0049] The precision positioning unit 60 is comprised of a global
navigation satellite system receiver, such as a triple
constellation concurrent GNSS receiver 86 and an Attitude and
Heading Reference System (AHRS: 3-axis gyroscope, 3-axis
accelerometer, and 3-axis magnetometer) 88. The GNSS receiver 86 is
a triple band receiver that is capable of tracking three (3)
constellations concurrently: GPS, GLONASS, and GALILEO. This
provides the GNSS receiver 86 with the best opportunity to lock
onto as many satellite vehicles as possible. This approach reduces
certain GNSS errors as it pertains to number of satellites in view
(satellite vehicles above a cutoff elevation angle), improved
Geometric Dilution of Precision (GDOP), and specifically access to
GALILEO, which offers improved Circular Error Probable (CEP) over
GPS and GLONASS.
[0050] The top level software states for the stimulus collar 30 are
depicted in state diagram 100, FIG. 4. In state 102, when the power
of collar 30 is turned on, software from memory 72, FIG. 3, is
loaded in microprocessor 70. In state 104 an initialization process
is instituted and a check of the various subsystems is carried out.
The initialization state is the first state the software enters
from any powered off state. In this state the software will set up
hardware communication channels with the peripherals and configure
each peripheral to a known state. The software will also read the
configuration parameters out of non-volatile storage.
[0051] Upon completion of the initialization steps, the software
will transition to the setup state 106. If setup has been
previously completed the system proceeds to run state 108 and, with
the collar on the pet, the system functions according to run state
diagram 120, FIG. 5, in the containment/tracking modes, as
described below. If setup has not been completed, then the system
proceeds to the main menu and the operator may select to proceed to
the learn mode (perimeter setup) and/or training mode, both of
which are depicted in FIG. 5.
[0052] From either the setup state 106 or the run state 108, in the
event of failure, the system transitions to error state 112 and
subsequently to hard off state 114. Also, from the set up state 106
or the run state 108 a hard off sequence may be initiated by the
user.
[0053] Referring to FIG. 5, run state diagram 120 includes learn
sub-state 122. When learn sub-state is activated a new perimeter is
learned and stored in memory 72 of processing unit 52, FIG. 3. The
software enters the learn sub-state when the operator elects to
define a new containment zone/perimeter. While in this state the
software turns on the display 76, AHRS 88, and GNSS receiver 86,
but leaves the cell modem 80 and Bluetooth radio 78 in a low power
state. The software collects waypoint data from the GNSS receiver
to form a perimeter, and at the conclusion of the process checks
the collected data for validity. If the points collected form a
valid perimeter, the data is stored in non-volatile memory.
[0054] Run state diagram 120 also includes a train sub-state 124
which is entered when a user trains the pet. This is done using a
fob or smart phone to manually issue static and/or audible
corrections so that the pet can learn the consequences of leaving
the defined containment zone. While in this state the cell modem 80
and display 76 are put into a low power state, while the Bluetooth
radio 78 is enabled to allow communication between the fob or smart
phone and collar 30. While in the train state the software will
enable the audible warning and correction circuit, if instructed to
via communication with the fob or smart phone. If the Bluetooth
link to the fob or smart phone is broken, the system will
transition into an open track state, as described below.
[0055] When the pet is trained and a containment area has been
saved and selected the system proceeds to the contain state 126, in
which case the collar 30 functions as described above to issue
audible and static corrections if the pet enters the warning zone
14 or out of bounds zone 16, respectively, of FIG. 1. If the pet
remains in the out of bounds zone for a predetermined time
(notwithstanding the issuance of a static correction), the system
transitions to the tracking state 128. When in tracking state 128
the Bluetooth radio 78 is powered down (if it was on), the cell
modem 80 and display 76 are enabled. The software continues to
monitor the animal's location in order to determine if it has
returned to the containment area. The software will alert the pet
owner through the cloud server that the animal has escaped the
containment area and will periodically send location and other
information (e.g. distance from the containment zone 10 and the
directions to the pet's then current location) via the cell modem
80 through the cloud server and subsequently to the operator's
smart phone.
[0056] If no perimeter has been selected and the user initiates
tracking mode the system will transition to the open track state
130, which does not perform a containment function but rather
performs the tracking function alone. The open track sub-state 130
maybe entered when the collar is in train sub-state 124 and the
Bluetooth link is broken and no perimeter has been selected. When
the system enters track sub-state 130 the Bluetooth radio 80 is
powered down, and the cell modem 80 and display 76 are enabled, as
well as the AHRS 88. The software continues to monitor the animal's
location via GNSS, and will continue to report the animal's
location through cellular link to the user's smart phone.
[0057] The operation of contain sub-state 126, FIG. 5, is shown in
more detail in FIG. 6 to include a number of lower sub-states as
depicted in contain sub-state diagram 140. The contain sub-state
may be activated at active state 142 or toggled into off state 144
according to state diagram 100 of FIG. 4. When in the active state
142, the system will move to the warn state 146 and issue an
audible correction when the pet enters warning zone 14, FIG. 1, and
either return to active state 142 if the pet retreats to the safe
zone 12 or proceed to correct state 148 and issue a static
correction if the pet proceeds to out of bounds zone 16. If in
response to the static correction the pet retreats to the safe zone
12 then the system returns to active state 142. If the pet does not
return to safe zone 12 after the static correction, then track
state 128, FIG. 5 is entered. If the pet subsequently returns to
the containment area, which is indicated at return to warn state
150 or return to correct state 152, the system reverts to active
containment state 142.
[0058] The system enters warn sub-state 146 when the position data
indicates the collar 30 has left the safe zone 12 and is in the
warning zone 14. The software will activate the audible alarm and
continue to monitor the location. If the reported position returns
to within the safe zone 12 the software turns off the audible alarm
and returns to active sub-state 142. If the reported position moves
out of the warning zone 14 and into the out of bounds zone 16, the
software transitions into the correct sub-state 148.
[0059] The software enters the correct sub-state 148 when the
position data indicates the collar is in out of bounds zone 16. The
software will activate the correction circuit (predetermined
timeout) and continue to monitor the location. If the reported
position returns to the warning zone 14 the software disables the
correction circuit and transitions into warn sub-state 146. If the
reported position returns to the safe zone 12 the software disables
the correction circuit and transitions into the active sub-state
142. In the event the animal remains in out of bounds zone 16, the
software disables the correction circuit and transitions out of
contain state and into the track state.
[0060] The return to warn sub-state 150/return to correct sub-state
152 exist to handle the case where the animal has left the
containment perimeter and was tracked, but has now returned to the
warning zone. In this instance the static and audible corrections
are not enabled, and the software continues to monitor the collar
location. If the GNSS position indicates the animal is within the
safe zone, the software transitions to the active sub-state 142. If
the position indicates the animal has left the warning zone and
entered the correction zone, the software transitions into the
Correct sub-state.
[0061] Additional detail will now be provided about configuring the
containment zone as well as position tracking of the pet in the
containment zone and outside of the containment zone.
Containment Zone Configuration
[0062] The system provides a method for the pet owner to create a
highly custom and accurate containment area comprised of GNSS
waypoints stored in onboard memory. The owner simply initiates a
Learn mode on the collar 30, walks the desired perimeter and saves
a custom map into memory. There can be several different maps
stored on collar 30 which may be selected by the user. The collar
30 will determine if the user generated a valid containment
perimeter and give a visual indication on display 34. Once a map is
activated, the collar 30 can be placed on the pet and the
self-contained containment system will run autonomously.
[0063] When collar 30 is powered on, the system will determine
whether it has valid ephemeris and almanac data. If the system does
not have valid ephemeris and almanac data, it will download new
data. The system is capable of receiving updated ephemeris and
almanac data through the cellular module 80. This is known as
Assisted Global Navigation Satellite System (aGNSS) where the
ephemeris and almanac data are transferred through cellular
networks at much higher speeds. Once the system acquires the new
and valid data, it will then begin obtaining satellite vehicles
through the tri-band GNSS antenna. Once the GNSS subsystem has
determined it has sufficient satellites in view, it will inform the
user through the display 34 that it is ready to collect waypoints
and begin creating a containment perimeter.
[0064] Flow diagram 160, FIG. 7, depicts the process for learn
state 122 of FIG. 5 to establish a customized containment
perimeter, such as perimeter 24 of FIG. 1. At step 162 the system
enters the learn state when the user has selected this state by
inputting a selection with buttons 36, FIG. 2. The user then
selects at step 164 whether to manually record the waypoints as the
collar 30 is walked along the perimeter or to have the system
automatically record waypoints as the collar 30 is walked along the
perimeter. If manual waypoint entry is selected at step 164, then
the user will press the indicated button 36 at step 166 and at step
168 a way point will be recorded. The waypoint is in the form of
longitudinal and latitudinal coordinates which are received from
GNSS module 86 of precision positioning unit 60 of FIG. 3. Record
waypoint step 168 is more fully described below with regard to FIG.
8. Once the waypoint is recorded, the user may continue to enter
waypoints at steps 166 and 168 until the user has completed walking
the perimeter and entering way points. By indicating at step 166
that no further waypoints will be entered, the system proceeds to
step 170 where the user is asked if she would like to exit learn
state/mode at which point the system exits the learn state/mode at
step 172.
[0065] If, alternatively, auto waypoint is selected at step 164,
then the user will press the indicated button 36 at step 174 and
way points will automatically recorded (e.g. once every second) at
step 168 as the user walks the perimeter. At step 174 the user can
select the appropriate button to indicate the perimeter walk has
been completed and then the system proceeds to step 170 where the
user is asked if she would like to exit learn state/mode at which
point the system exits the learn state/mode at step 172. It should
be noted that while using the auto waypoint function, if the user
encounters an obstacle a pause button may be pressed while the user
walks around the obstacle and then the pause can be removed and the
waypoint recording will continue. The last waypoint before pause
was selected and after recording is resumed will be connected with
a straight line through the obstacle.
[0066] Flow chart 180, FIG. 8A, depicts the record waypoint process
in more detail. At step 182 a waypoint, P, is made available either
through manual selection or automatic selection as described in
flow chart 160, FIG. 7. At step 184, the current waypoint is
evaluated to determine if it is a sufficiently accurate waypoint.
To determine if a minimum level of accuracy is present, the HDOP
(horizontal dilution of precision) and/or PDOP (precision and
positional dilution of precision) values, which are received from
GNSS module 86, may be evaluated, for example. If the minimum
values are not met, the system proceeds to step 186 where operation
is returned to flow chart 160 for the selection of the next
waypoint. If the minimum values are met at step 184, the system
proceeds to step 188 where the distance (dD) from the previous
waypoint to the current waypoint is calculated. If at step 190, the
distance dD is less than a minimum value (MinDelta), the system
proceeds to step 186 where operation is returned to flow chart 160
for the selection of the next waypoint. If the distance dD is
greater than a minimum value (MinDelta), at step 192 the waypoint
is linearized. The minimum value is set to ensure that the distance
between waypoints is sufficient to form a discernible line segment
given the system resolution. At step 194, it is determined if the
waypoint is co-linear, then at step 196 the waypoint is stored in
waypoint array at point P-1 as a waypoint for the containment
perimeter being established. If it is determined that the waypoint
is not co-linear then at step 198 the waypoint P is stored in
another array.
[0067] The system then proceeds to step 186 where operation is
returned to flow chart 160 for the selection of the next
waypoint.
[0068] For each waypoint recorded where the point count is greater
than 2, a test will be employed to determine if the variance from a
straight line for the new waypoint is sufficiently small to warrant
the replacement of the n-1 point with the then new point,
effectively straightening the line.
[0069] The same calculation will be used for determining the
distance of a containment point to containment perimeter. To
calculate a distance from a point to a line where P3,P4 is
perpendicular to P1,P2:
p1=x1,y1
p2=x2,y2
p3=x3,y3
p4=x4,y4
mu=((x3-x1)(x2-x1)+(y3-y1)(y2-y1))/(.parallel.p2-p1.parallel.).sup.2
[0070] mu between 0 and 1 indicates intersection [0071] distance
then is x3,y3 to x4,y4 (on the line segment)
[0071] x4=x1+mu(x2-x1)
y4=y1+mu(y2-y1)
distance= {square root over ((x4-x3).sup.2+(y4-y3).sup.2)}
[0072] As depicted in FIG. 8B, consider this situation where W1 and
W2 have already been recorded in the array as the prior two
waypoints, W3 is the new waypoint, and P4 will be calculated to
determine the distance W2 to P4. The above algorithm can then be
used, substituting:
P1=W1, P2=W3, P3=W2
mu=((W2x-W1x)(W3x-W1x)+(W.sup.2y-W1y)(W3y-W1y))/((.parallel.W3-W1.parall-
el.) 2)
P4x=W1x+mu(W3x-W1x)
P4y=W1y+mu(W3y-W1y)
[0073] And, solving for the distance:
=sqrt((P4x-W2x) 2_(P4y-W2y) 2)
[0074] If the distance is less than a predefined epsilon, then W1,
W2, W3 can be considered collinear and the W3 waypoint substituted
for W2.
[0075] As described, the co-linear points stored in array P-1, may
be reduced to reduce the number of line segments produced in the
overall containment perimeter. Since the MinDelta distance
criterion is already met, we deem that if a point is co-linear we
can replace the previous co-linear point with the new one in order
to reduce the number of line segments from two to one taken out to
n points. This helps to reduce the number of points taken for
memory optimization.
[0076] The waypoints saved which are not co-linear are still valid
waypoints. For example, the user, when developing the perimeter,
could have made an intentional move to avoid an object or make a
turn and thus the point is not co-linear. When this is the case, we
must keep it as part of the perimeter. This array is for points
taken that are not co-linear and a bucket of points that signify a
change in direction. When all way points have been collected and
processed, the co-linear way points are merged with the way points
which are not co-linear to form the full containment perimeter.
[0077] Referring now to flow chart 200, FIG. 9, exit step 172 of
flow chart 160, FIG. 7 is described in more detail. The process
described by flow chart 200 determines whether the set of waypoints
collected to form a desired containment perimeter is a good/closed
or properly formed perimeter, i.e. a perimeter which is in the
shape of a polygon. The containment area can be as large and have
as many sides as desired as long as the polygon does not intersect
itself.
[0078] At step 202, it is determined if the total number of
waypoints collected and in the waypoint array exceeds two. If it
does not then the waypoint array is discarded and an error message
is provided to the user at step 204. If total number of waypoints
collected exceeds two, at step 206, each segment formed by the
waypoints (P-1, P) is tested against all other segments to see if
there are any segment intersections. If at step 208, it is
determined that there is at least one segment intersection the
waypoint array is discarded and an error message is provided to the
user at step 204. If there are zero segment intersections, then at
step 210 the array of waypoints is stored in nonvolatile memory 72
of processing unit 52, FIG. 3, as a containment map for use by the
user and the system exits at step 212 and returns to the main menu
and waits for the user to select a function.
Way Point Error Reduction
[0079] Traditionally with GNSS receivers, there are inherent
positional errors due to atmospheric influences, satellite
geometries and DOPs, and local multipath environment. Since
satellites orbit the earth 2 times in a span that is slightly less
than twenty four (24) hours, for any given point on earth, or
latitude and longitude, the error will change over that time having
a maximum error value and minimum error value. The satellites will
rise and set about 4 minutes earlier each day. As such at any given
point on earth's surface, it will repeat the same error two times
in one day.
[0080] This becomes an issue when the user is going to define a
containment perimeter because it will be the expected perimeter
used from that point on at their primary residence or any other
location they may take it. Thus, the waypoints recorded when the
user establishes a containment perimeter may have errors that could
result in the formation of an unintended perimeter of the
containment area if the time the waypoints are recorded coincides
with the time varying errors inherent in the GPS or other satellite
systems described above. The user cannot be limited to generating a
containment perimeter at only specific times during the day, a
method to reduce inherent and arbitrary GNSS errors at any given
time must be provided.
[0081] A preferred method for reducing waypoint errors is called
the "saw tooth" method. For any given point or straight line, there
will be an associated error or distance offset from that point or
straight line. Typically when setting a containment perimeter the
user will walk in straight lines or curves. The calculated GNSS
position could be Z meters (e.g., up to several meters) away from
the "true" position at any given time due to the above-described
positional errors. To illustrate this, referring to FIG. 10, if the
user walks a straight line, line Y, for 30 meters at a point in
time, the calculated GNSS straight line, line X, could have a
constant offset or constant positional error delta of Z meters
during the entire walk of 30 meters.
[0082] This, of course, could cause a significant problem. For
example, a pet owner may want to use a visible part of the yard
(e.g. where the grass meets the edge of the driveway or road) as a
part of the containment perimeter. If where the grass meets the
driveway/road is the visible "true" indicator of where the pet
owner walked in establishing the containment perimeter, then the
calculated GNSS position could have an error, Z meters. This could
place the perimeter of the containment area in the middle of the
driveway or worse yet the road.
[0083] The above described error can be compounded over time. As
satellites orbit the earth, they are moving the GNSS error line
which can cause the noted error, Z, to be larger and smaller
causing a high variability over the course of time. These
conditions can occur during turns onto different portions of the
intended containment perimeter. For example, if the user intends to
walk a square for their containment perimeter, they will start
walking in a straight line and the GNSS system accurately places
them on that intended line. However, with DOPs (dilution of
precision) and local multipath influences, when the user turns
right or left onto the next leg of the perimeter, the GNSS system
may overshoot or undershoot the intended turn. This over-shoot or
undershoot then becomes the Z-meter offset. Since the user will
tend to continue to walk in a straight line, the GNSS system will
never correct the error offset because it is predicting the next
location based on previous location, Speed over Ground (SoG) and
Course over Ground (CoG), values.
[0084] With GNSS systems, there are several bits of data that come
out of the National Marine Electronics Association (NMEA) message
string. Two important pieces of data are the Course over Ground
(CoG) and Speed over Ground (SoG) values. Known GNSS systems can
accurately predict the location of a moving object by knowing the
previous CoG value, heading relative to North, and SoG value, speed
in meters/second.
[0085] To compensate for this error, the user may make an action to
force the GNSS system to change CoG. By changing direction the GNSS
must then account for changes in CoG. In order to correct for this
offset error over time and reduce the overall variability, the GNSS
receiver must cross the intended "true" perimeter 218 several times
to average out the error. This may be accomplished by having the
user walk across the intended containment perimeter in a saw tooth
pattern (i.e. each segment crosses the intended perimeter 218 at an
angle), such as pattern 220 shown in FIG. 11, in order to average
out the error.
[0086] The saw tooth approach can be incorporated into the logic
described above for waypoint recording by taking the actual
waypoints collected for the end points (e.g. 222 and 224) of each
saw tooth segment (e.g. 226) and taking the average distance
between the two end points of each saw tooth segment. These end
points are waypoints taken in latitude and longitude to determine
the halfway point. Once the user completes the walk (or completes
the containment perimeter) the perimeter can then be `drawn" using
the averages of the end points (e.g. average point 230). The two
end points of each section are recognized by detecting a change in
direction which is determined from the waypoints. Once the change
in direction occurs, the latitude and longitude values are saved in
temporary memory and used to calculate the halfway point between
the two as follows:
WayPoint 1=WP1=(latitude, longitude)
WayPoint 2=WP2=(latitude, longitude)
New WayPoint=NWP=(latitude, longitude)
Let WP1=42.928521, -71.532675
Let WP2=42.928534, -71.532730
Therefore,
NWP=(WP1+WP2)/2
=((42.928521+42.928534), (-71.532675+-71.532730))/2
=((85.857055), (143.065405))/2
NWP=(42.928527, -71.532702)
The full equation with n number of samples within the containment
perimeter then becomes:
(WP1+WP2)/2=NWP1,(WP2+WP3)/2=NWP2,(WP3+WP4)/2=NWP3, for n
samples
[0087] This method can be verified using standard map tools to show
that the new or average way point does indeed bisect the two way
points taken at the end points of the saw tooth segment. Therefore,
when the user finishes walking the perimeter, a containment map
will have been developed with error compensation. This approach
reduces the overall error at any given time, thus producing a map
that is more accurate than one that is comprised of just real-time
way points from the GNSS output.
Position Tracking
[0088] Once a containment perimeter has been established and
selected to contain a pet, the containment state/mode may be
activated by the user. In this mode, the system must be able to
quickly and accurately determine if the pet is in the safe zone 12,
warning zone 14, or out of bounds zone 16 of FIG. 1. The GNSS
module 86 tracks three constellations and operates at a 3 Hz Output
Data Rate (ODR). This ODR is sufficiently fast, but to be a very
effective GNSS containment system, there needs to be a predictive
element to ensure the pet stays within the safe zone. The preferred
embodiment of the invention uses a ray casting technique to
determine the location of the pet with respect to the containment
area at any given time.
[0089] To describe this approach, referring to FIGS. 12A and 12B,
we start with determining the plane in which the containment zone
polygon lies by using two non-parallel edges to compute the normal
to the plane:
n=(v1-v0).times.(v3-v0)/.parallel.(v1-v0).times.(v3-v0).parallel.
[0090] and a vertex applied to complete the plane definition,
p=v0
[0091] Therefore, the distance of any point x from the plane of the
polygon is:
d=(x-p)*n [0092] and the plane equation then becomes,
[0092] (x-p)*n=0
Based on this geometric model, the plane in which the polygon lies
has been determined. Each line segment can be constructed and
converted to Local Tangent Plane (LTP) of the Earth Centered Earth
Fixed (ECEF) coordinate system. Using this method, the output from
the GNSS receiver system, latitude and longitude, can be used to
figure a position Pr (see FIG. 12B), cast a ray to the nearest line
segment, and predict the direction of a potential breach of the
containment perimeter.
[0093] Using these principles, it can be determined quickly and
accurately if the pet has breached the containment area and, if so,
a notification alert can be immediately sent to the smart device of
the owner and the system can transition to tracking mode to monitor
the position of the pet. More specifically, the system casts a ray
that intersects with the polygon (containment area) in two simple
steps: First the ray-plane intersection x is determined and then
simply it is determined whether x is inside or outside the polygon.
For this the general ray equation is used:
x=Pr+t(Ur)
[0094] t, the number of times the ray crosses the polygon, is
determined.
[0095] Therefore, for the ray-plane intersection we can replace x
with the plane equation from above:
t=((P-Pr)*n)/(Ur*n)
If t<0 then there is no intersection of the polygon. If t>0,
then there is an intersection at:
x=Pr+t(Ur)
[0096] From this the number of times the ray crosses the polygon is
determined. With this information we can then determine whether x
(the pet) is inside or outside of the polygon. Note that the
polygon vertices and point both lie on the same plane and therefore
makes them planar. As such, if we cast a ray to the closest edge of
the simple polygon, we can determine if the point is inside or
outside the polygon by determining the number of times the ray
crosses the polygon. If the number of crosses is odd (1, 3, 5,
etc.), the point (pet) lies within the polygon. If the number is
even (0, 2, 4, etc.), the point (pet) lies outside of the
polygon.
[0097] When the pet is in the safe zone, there is a "Distance to
Edge" calculation that is performed to determine if the pet is in
the warning zone. If the Distance to Edge number is less than 3
meters (or other designated distance defining the perimeter of the
warning zone), the system knows that the pet is in the warning zone
and the static/audible correction unit 58 (FIG. 3) issues an
audible correction to warn the pet that it is approaching the
perimeter of the containment area.
[0098] With this method, the preferred embodiment can quickly and
reliably determine if the pet is in the safe zone, warning zone, or
out of bounds zone. This approach is illustrated in FIG. 13 where
containment perimeter 250 is shown to form safe zone 252. While a
warning zone would be included, for simplicity it has been omitted
from this example. In one example, ray 254 extending from location
256 in the direction of the closest portion 258 of the perimeter is
shown to cross perimeter 250 at point 258, point 260 and at point
262, for a total of three crossing points. Since the number of
crossing points is odd, the system will know that the pet at
location 256 is in the safety zone 252. In another example, ray 270
extending from location 272 in the direction of the closest portion
274 of the perimeter is shown to cross perimeter 250 at point 274,
point 276, point 278, and point 280, for a total of four crossing
points. Since the number of crossing points is even, the system
will know that the pet at location 272 is in the out of bounds zone
281.
[0099] As indicated by rays 282 and 284 (shown in phantom) it is
not a requirement that the ray be cast to the closest portion of
perimeter 250 from the locations 256 and 272. As depicted, rays 282
and 284 intersect perimeter 250 three (odd) and four (even) times,
respectively, just as did rays 254 and 270.
[0100] Also shown in FIG. 13 is a second out of bounds zone 290
(such as a pond) having a perimeter 291 contained within safe zone
252. At location 292 a ray 294 is cast and intersects three points,
two in perimeter 291 and one in perimeter 250, indicating that
location 292 is in a safe zone. At location 296 a ray 298 is cast
and intersects two points, one in perimeter 291 and one in
perimeter 250, indicating that location 296 is in out of bounds
zone 290.
GNSS Walking Error Correction
[0101] To accurately and effectively use the ray casting approach
described above, the "true" GNSS position/coordinates of the pet
must be known at all times during operation. If the raw, real-time
output of the GNSS system is used, the system would be subject to
the real-time errors. In order to correct for real-time errors, the
real-time stream of GNSS positioning information is augmented with
data from the Attitude and Heading Reference System (AHRS) 88 of
the precision positioning unit 60. Moreover, the following approach
can be used in the tracking mode as well to more accurately locate
the position of the pet.
[0102] With GNSS systems, there are several bits of data that come
out of the National Marine Electronics Association (NMEA) message
string. Two important pieces of data are the Course over Ground
(CoG) and Speed over Ground (SoG) values. Known GNSS systems can
accurately predict the location of a moving object by knowing the
previous CoG value, heading relative to North, and SoG value, speed
in meters/second.
[0103] In addition, we track SoG and CoG for speed and heading and
use the AHRS to compensate for any heading errors due to severe
multipath of satellite signals. SoG and CoG are part of the GNSS
data string; they come with every waypoint. We use the Gyroscope
and Magnetometer in the AHRS to double check the CoG from the GNSS
and double check whether the pet is moving or stationary. With GNSS
systems, it is known that when the object/GNSS receiver is
stationary, the subsequent calculated positioning information tends
to "walk" around even though the receiver is motionless.
[0104] Such "walking" errors are due to the fact that the
satellites in orbit continue to move as the receiver is stationary.
This causes significant inaccuracies in the GNSS computation of
where it is on earth. With these errors, when the pet is
stationary, the GNSS module 86 may be outputting coordinates
indicating that the pet is several meters away from its actual
location. If the pet was stationary near a house or other
reflective structure, that error would increase and potentially put
the pet in the warning zone or out of bounds zone, and the pet
would receive a correction even when it was really in the safe
zone.
[0105] In the preferred embodiment, a method is used to augment
real-time GNSS data and implement hysteresis to improve overall
location accuracy of the collar by using the AHRS subsystem to
determine whether the pet is in motion or stationary. Further
enhancing the accuracy of the system is implementing hysteresis
after the pet has left a no motion state.
[0106] The AHRS subsystem runs on an Attitude Engine and Extended
Kalman Filter to provide the most accurate sensor data output. The
filtered accelerometer output can be used in conjunction with the
SoG value output from the GNSS and can reliably determine if the
pet is in motion or stationary. However, in order to do that
accurately, gravity compensation on the accelerometer of the AHRS
subsystem must be performed. Accelerometers, due to their nature,
measure both gravitational and linear acceleration in m/s/s. Here,
only linear acceleration is needed, which we can then derive a
linear displacement of the pet if it actually moved. Because
accelerometers are not influenced by multipath signals, it provides
the advantage of using it as a filter mechanism for the SoG value
from the GNSS system because as multipath signals are observed,
there will also be a SoG value>0 m/s that will also be
observed.
[0107] The AHRS outputs raw acceleration which is the combined
effect of acceleration due to gravity and any linear displacement.
It is then necessary to subtract out the acceleration forces due to
gravity thus leaving only linear acceleration. To do this, the AHRS
has quaternion outputs q0, q1, q2, and q3 that are not affected by
multipath effects. With these quaternion outputs one can perform
quaternion math to subtract out the gravity vector in the raw
acceleration values provided by the AHRS. Gravity compensation can
be achieved by the following set of equations:
[0108] We first must obtain the direction of gravity in each axis
where the quaternion output from the AHRS is referenced to LTP
giving:
g(x)=2*(q1*q3-q0*q2);
g(y)=2*(q0*q1+q2*q3);
g(z)=q0*q0-q1*q1-q2*q2+q3*q3; [0109] which provides results of
g(x), g(y), and g(z) as unit vectors.
[0110] The unit vectors now must be scaled properly which can
simply be done by:
g(x)_scaled=g(x)_raw/9.81
g(y)_scaled=g(y)_raw/9.81
g(z)_scaled=g(z)_raw/9.81
And finally we can achieve gravity compensated acceleration by:
g(x)_comp=(g(x)_scaled-g(x))*9.81
g(y)_comp=(g(y)_scaled-g(y))*9.81
g(z)_comp=(g(z)_scaled-g(z))*9.81
Now with linear acceleration only, it can be compared to the SoG
value from the GNSS and accurately determine if the pet is in
motion or stationary. This is highly critical when it comes to the
accuracy of the system because as we know the GNSS information
unfiltered tends to "walk" causing greater inaccuracies. With this
critical information we can now combine augmentation and averaging
techniques to the GNSS system and achieve greater accuracy.
[0111] This process is shown in flow chart 300, FIG. 14. In step
302 it is determined each time period, t, if the pet is in motion,
as described above, and at step 304 the GNSS real-time data output
is used to accurately track the pet position using ray casting.
[0112] If at step 302 it is determined that the pet is not in
motion, then at step 306 the next n samples, one obtained each of
the next n time periods t of GNSS data, are averaged and at step
308 the system freezes the pet location at the averaged position.
While the pet is not in motion, all subsequent positioning data
from the GNSS is ignored and the pet's position is locked at the
position corresponding to the average of the n samples. The system
continues to check for pet movement at step 310 and if the pet
continues to be stationary the position continues to be locked at
step 308. If it is determined that the pet has begun to move again
at step 310, the system reverts to position location using ray
casting at step 304.
[0113] Therefore, the sequence of events as motion and no motion
occur is the following: [0114] Pet=in motion: Maintain real-time
GNSS feed and monitor AHRS to determine if pet has stopped moving.
[0115] Pet=no motion: Flag no motion state, gain an average of n
samples and lock position. This becomes new "true" position
relative to the containment perimeter and ray cast distance is
updated. [0116] Pet=in motion after no motion: Flag motion state,
implement hysteresis due to multipath (i.e. ignore initial new GNSS
feed position readings to allow system to settle to more accurate
readings after motion begins again), maintain real-time GNSS feed
and monitor AHRS to determine if pet has stopped moving.
[0117] By using this method to accurately track the pet, it reduces
the overall errors inherent in GNSS systems. It also provides a
method to reduce local multipath errors which can be highly
variable depending on the environment. As stated earlier, when the
pet is near highly reflective objects like homes or urban canyons,
the pet's position will move around even when it is not in motion.
The error case is much larger in urban canyons where highly
reflective glass material and tall buildings exists which can
introduce errors in the tens or even hundreds of meters. To
mitigate these errors whether in the containment perimeter or
otherwise; the positioning engine will lock the position of the pet
when it has sensed no motion. This prevents subsequent GNSS
readings from moving the pet around when in reality it has not
moved at all.
Adjustment for Structures in Containment Area
[0118] One major issue with GNSS systems is that when they are for
positioning objects under structures, such as in homes, the signal
quality is highly degraded and the positioning accuracy cannot be
relied upon. With the preferred embodiment, a home, garage or
another structure may be used as part of the containment
perimeter.
[0119] As shown in FIG. 15 containment area 320 includes a house
322 as part of the containment perimeter 324. In this example the
pet owner started on one side 326 of house 322 and ended on the
opposite side 328 to complete the containment perimeter 324.
Because the ray casting algorithm needs to cast to a simple
polygon, the system automatically connects the start point 326 with
the endpoint 328 by drawing a straight line.
[0120] Without implementing the adjustments according to this
invention, if the pet walked into the garage or house and breached
the perimeter that is drawn across the home, it would receive an
audible and also a static correction. This is highly undesirable
for the pet as the pet should be able to enter/exit the home freely
without receiving corrections.
[0121] This is achieved by assessing the NMEA message string of all
satellites that the GNSS receiver is in communication with and
obtaining the Carrier-to-Noise (C/N0) ratio of each satellite. The
system then averages all the C/N0s together to get the average C/N0
ratio. When the pet is outside and has view of most of the sky, the
C/N0 values will be high and exceed a predetermined high threshold.
As long as the total averaged C/N0 value remains above this
threshold, the system will deem that the pet is outside and remains
in normal containment operation.
[0122] In the event the pet walks inside the garage or home, the
structure will severely attenuate the C/N0 value. The system will
have a predetermined low threshold to indicate that the pet is
indoors. If the threshold is crossed, the system will determine
that the pet is indoors and the system will virtually "place" the
pet in the containment perimeter 324 (e.g. proximate the center),
notwithstanding its actual position, in order to prevent invalid
corrections. The first and second thresholds are typically
different values. In the event the pet does walk out of the
house/garage and the C/N0 values exceed the high threshold for a
minimum amount of time, the collar will deem the pet to be outdoors
and will resume normal mode of operation.
[0123] This ensures the pet can safely enter/exit the homes and
garages that have been intended to be part of the containment
perimeter.
[0124] The logic flow in the method is as follows:
Total averaged C/N0>high threshold=pet is outdoors, normal
containment perimeter.
Total averaged C/N0<low threshold=pet is indoors, normal
containment perimeter, pet location is placed in center of
containment perimeter.
[0125] By using this method, pet owners now have the ability to use
their homes and garages as part of the containment perimeter. It
offers an incredibly convenient, low cost, flexible, and highly
custom method to develop a containment perimeter that blocks off
either the front or back of the yard without routing needless wire
into the ground and allows the pet to enter/exit the home/garage
without receiving an audible/static correction.
[0126] Having described the invention, and a preferred embodiment
thereof, what is claimed as new and secured by letters patent
is:
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