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Claims  |
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I claim:
1. Apparatus for monitoring adherence of a vehicle to a selected vehicle
route from a vehicle monitoring station, the apparatus comprising:
location determination (LD) means, carried on a selected vehicle, for
receiving LD signals from an LD signal source spaced apart from the
vehicle and for determining and recording the location coordinates
corresponding to a location L(t.sub.s) of the vehicle at a selected time
t=t.sub.s ;
a computer, carried on the vehicle and communicating with the LD means,
having an electronic map of a selected route R, where the selected route
is approximated by an ordered sequence {P.sub.k }.sub.k of path segments
P.sub.k, numbered k=1,2, . . , K (K.gtoreq.2), with path segment P.sub.k'
(1.ltoreq.k'<K) being intersected by path segment P.sub.k'+1, in at least
one point and with each path segment P.sub.k being surrounded by a
corridor segment C.sub.k having a width approximately equal to 2d.sub.k,
measured in a direction approximately perpendicular to a general direction
of the segment P.sub.k, where d.sub.k is a selected positive distance;
where the computer determines the perpendicular foot .pi..sub.k
(L(t.sub.s)) of the location L(t.sub.s) on at least one of the path
segments P.sub.k, determines the distance D.sub.k (L(t.sub.s)) from the
location L(t.sub.s) to the perpendicular foot .pi..sub.k (L(t.sub.s)), and
determines whether the distance D.sub.k (L(t.sub.s)).ltoreq.d.sub.k for at
least one index value k;
where the computer determines that, when D.sub.k
(L(t.sub.s)).ltoreq.d.sub.k for at least one index value k, the vehicle is
adhering to the selected route R; and
where the computer determines, when D.sub.k (L(t.sub.s))>d.sub.k for all
index values k, that the vehicle is not adhering to the route R, and the
computer then transmits at least one of (1) a signal indicating that the
vehicle is not adhering to the route R and (2) the location coordinates of
the vehicle for at least one selected time t=t.sub.s', for which D.sub.k
(L(t.sub.s'))>d.sub.k, to a selected vehicle monitoring station that is
spaced apart from the vehicle.
2. The apparatus of claim 1, wherein, when said computer determines that
said vehicle is not adhering to said route R, said computer transmits, to
a selected vehicle monitoring station that is spaced apart from said
vehicle, at least one of: (1) a signal indicating that said vehicle is not
adhering to said route R and (2) the location coordinates of said vehicle
for at least one of said selected times t=t.sub.s' for which D.sub.k
(L(t.sub.s'))>d.sub.k.
3. The apparatus of claim 1, further comprising display means, connected to
said computer, for displaying said present location L(t.sub.s) of said
vehicle and for displaying at least one of said path segments P.sub.k that
provide an approximation to said selected route,
wherein said computer includes a snap-to-route switch that, when activated,
replaces said present location L(t.sub.s) of said vehicle by a
perpendicular foot .pi..sub.k,min (L(t.sub.s)) of said present location on
one of said path segments, P.sub.k,min where said distance D.sub.k,min
(L(t.sub.s))=min.sub.k D.sub.k (L(t.sub.s)), and displays the location of
the perpendicular foot .pi..sub.k,min (L(t.sub.s)) on said path segment
P.sub.k,min.
4. The apparatus of claim 3, wherein, when said snap-to-route switch is
activated:
said computer expresses any spatial location in terms of Cartesian
coordinates (x,y,z), and said computer represents, and said display means
displays, said present location L(t.sub.s) by a Cartesian coordinate
triple (x(L(t.sub.s)), y(L(t.sub.s)), z(L(t.sub.s))); and
said computer represents, and said display means displays, a line L.sub.k
that passes through said present location L(t.sub.s) and passes
perpendicularly through a plane containing said path segment P.sub.k by an
equation x(L(t.sub.s)) cos .theta..sub.x,k +y(L)t.sub.s)) cos
.theta..sub.y,k +z(L(t.sub.s)) cos .theta..sub.z,k [=K.sub.k
(L(t.sub.s))]-p.sub.k =-D.sub.k (L(t.sub.s)), where cos .theta..sub.x,k,
cos .theta..sub.y,k and cos .theta..sub.z,k, are the direction cosines of
the normal to this plane containing said path segment P.sub.k, where
P.sub.k is the perpendicular distance from the origin to this plane
containing said path segment P.sub.k, and where D.sub.k (L(t.sub.s)) is
the length of a segment of the line L.sub.k extending from said present
location L(t.sub.s) to a point .pi..sub.k (L(t.sub.s)) on said path
segment P.sub.k.
5. The apparatus of claim 1, wherein
said computer expresses any spatial location in terms of Cartesian
coordinates (x,y,z);
said computer expresses the location of said vehicle at a first selected
time t=t.sub.1 in terms of the Cartesian coordinates
(x(t.sub.1),y(t.sub.1),z(t.sub.1));
said computer determines average velocity components
(v.sub.x,avg,v.sub.y,avg,v.sub.z,avg) for said vehicle parallel to the
Cartesian coordinate axes for a time interval t.sub.2
.ltoreq.t.ltoreq.t.sub.1, where t.sub.2 is a second selected time that is
less than t.sub.1 ; and
said computer estimates the coordinates of said present location L of said
vehicle for a selected present time t>t.sub.1 by the equations
x(t)=x(t.sub.1)+v.sub.x,avg (t--t.sub.1),
y(t)=y(t.sub.1)+v.sub.y,avg (t--t.sub.1), and
z(t)=z(t.sub.1)+v.sub.z,avg (t--t.sub.1).
6. The apparatus of claim 1, wherein
said computer expresses any spatial location in terms of Cartesian
coordinates (x,y,z);
said computer expresses the location of said vehicle at a first selected
time t=t.sub.1 in terms of the Cartesian coordinates
(x(t.sub.1),y(t.sub.1),z(t.sub.1));
said computer determines average velocity components
(v.sub.x,avg,v.sub.y,avg,v.sub.z,avg) for said vehicle parallel to the
Cartesian coordinate axes for a time interval t.sub.2
.ltoreq.t.ltoreq.t.sub.1, where t.sub.2 is a second selected time and is
less than t.sub.1 ;
said computer determines average acceleration components (a.sub.x,avg,
a.sub.y,avg, a.sub.z,avg) for said vehicle parallel to the Cartesian
coordinate axes for a time interval t.sub.3 .ltoreq.t.ltoreq.t.sub.1,
where t.sub.3 is a third selected time and is less than t.sub.1 ; and
said computer estimates the coordinates of said present location L of said
vehicle for a selected present time t>t.sub.1 by the equations
x(t)=x(t.sub.1)+v.sub.x,avg (t--t.sub.1)+a.sub.x,avg (t--t.sub.1).sup.2 /2,
y(t)=y(t.sub.1)+v.sub.y,avg (t--t.sub.1)+a.sub.y,avg (t--t.sub.1).sup.2 /2,
and
z(t)=z(t.sub.1)+v.sub.z,avg (t--t.sub.1)+a.sub.z,avg (t--t.sub.1).sup.2 /2.
7. The apparatus of claim 1, wherein
said computer expresses any spatial location in terms of Cartesian
coordinates (x,y,z);
said computer expresses the location of said vehicle at a first selected
time t=t.sub.1 in terms of the Cartesian coordinates
(x(t.sub.1),y(t.sub.1),z(t.sub.1));
said computer determines average direction cosine components of the vehicle
velocity (cos .theta..sub.vx,avg, cos .theta..sub.vy,avg, cos
.theta..sub.vz,avg) parallel to the Cartesian coordinate axes or a time
interval t.sub.2 .ltoreq.t.ltoreq.t.sub.1, where t.sub.2 is a second
selected time that is less than t.sub.1 ;
said computer measures the cumulative distance .delta.(t) said vehicle has
moved at the first selected time t=t.sub.1 and at a selected present time
t>t.sub.1 ; and
said computer estimates the coordinates of said present location L of said
vehicle for the time t by the equations
x(t)=x(t.sub.1)+[.delta.(t)-.delta.(t.sub.1)] cos .theta..sub.vx,avg
(t--t.sub.1),
y(t)=y(t.sub.1)+[.delta.(t)-.delta.(t.sub.1)] cos .theta..sub.vy,avg
(t--t.sub.1), and
z(t)=z(t.sub.1)+[.delta.(t)-.delta.(t.sub.1)] cos .theta..sub.vz,avg
(t--t.sub.1).
8. The apparatus of claim 1, wherein
said computer expresses any spatial location in terms of Cartesian
coordinates (x,y,z);
said computer expresses the location of said vehicle at a first selected
time t=t.sub.1 in terms of the Cartesian coordinates
(x(t.sub.1),y(t.sub.1),z(t.sub.1));
said computer determines average direction cosine components of the vehicle
velocity (cos .theta..sub.vx,avg, cos .theta..sub.vy,avg, cos
.theta..sub.vz,avg) parallel to the Cartesian coordinate axes for a time
interval t.sub.2 .ltoreq.t.ltoreq.t.sub.1, where t.sub.2 is a second
selected time that is less than t.sub.1 ;
said computer measures the velocity v(t) at which said vehicle is moving
for a sequence of times between the first selected time t=t.sub.1 and a
selected present time t>t.sub.1 ; and
said computer estimates the coordinates of said present location L of said
vehicle for the time t by the equations
##EQU3##
9. The apparatus of claim 1, wherein said LD means is part of a location
determination system that is drawn from the group of location
determination systems consisting of Global Positioning System, Global
Orbiting Navigational Satellite System, Loran, Omega, Decca, Tacan, JTIDS
Relnav and Personal Location Reporting Service, where said LD means has an
LD signal antenna to receive said LD signals from said LD signal source
and has an LD signal receiver/processor to receive said LD signals from
the LD signal antenna and to determine the present location of the LD
signal antenna from said LD signals.
10. Apparatus for monitoring adherence of a vehicle to a selected time
schedule along a selected vehicle route from a vehicle monitoring station,
the apparatus comprising:
location determination (LD) means, carried on a selected vehicle, for
receiving LD signals from an LD signal source spaced apart from the
vehicle and for determining and recording the location coordinates
corresponding to a location L(t.sub.s) of the vehicle at a selected time
t=t.sub.s ;
a computer, carried on the vehicle and communicating with the LD means,
having a selected time schedule for the vehicle stored therein, where the
time schedule is represented by at least one ordered time schedule triple
(TI.sub.n,L.sub.n,d.sub.n) in an ordered sequence
{(TI.sub.m,L.sub.m,d.sub.m)}.sub.m of one or more time schedule triples of
values, where TI.sub.n ={t.vertline.t.sub.n-.DELTA.t.sub.n
.ltoreq.t.ltoreq.t.sub.n +.DELTA.t.sub.n } is a selected time interval,
with t.sub.n and .DELTA.t.sub.n being selected times and with
.DELTA.t.sub.n >0, L.sub.n is a selected location in a region through
which the vehicle passes, and d.sub.n is a selected positive number;
where the LD means and computer are used to determine, for a sequence of
one or more selected times t=t'.sub.r,u in an ordered sequence {t'.sub.r,v
}.sub.v of such times, lying in a chosen time schedule time interval
TI.sub.r with associated selected location L.sub.r, the location
L(t'.sub.r,u) of the vehicle at the time t=t'.sub.r,u, to determine the
distance between the location L.sub.r and the location L(t'.sub.r,u), and
to determine whether the distance between the location L.sub.r and the
location L(t'.sub.r,u) satisfies the relation distance .vertline.L.sub.r
-L(t'.sub.r,u).vertline..ltoreq.d.sub.r for at least one selected time
t'.sub.r,u in the time interval TI.sub.r ;
where the computer determines that, when the relation distance relation
.vertline.L.sub.r -L(t'.sub.r,u).vertline..ltoreq.d.sub.r is satisfied for
at least one selected time t'.sub.r,u in the time interval TI.sub.r, the
vehicle has adhered to the selected time schedule in the time interval
TI.sub.r ; and
where the computer determines that, when the relation distance relation
.vertline.L.sub.r -L(t'.sub.r,u).vertline..ltoreq.d.sub.r is not satisfied
for any selected time t'.sub.r,u in the time interval TI.sub.r, the
vehicle has not adhered to the selected time schedule in the time interval
TI.sub.r.
11. The apparatus of claim 10, wherein, when said computer determines that
said vehicle is not adhering to said selected time schedule in said time
interval TI.sub.r, said computer transmits, to a selected vehicle
monitoring station that is spaced apart from said vehicle, at least one
of: (1) a signal indicating that said vehicle has not adhered to said
selected time schedule in said time interval TI.sub.r , and (2) said time
interval TI.sub.r and said associated location L.sub.r for which said
vehicle has not adhered to the selected time schedule in said time
interval TI.sub.r.
12. The apparatus of claim 10, wherein said LD means is part of a location
determination system that is drawn from the group of location
determination systems consisting of Global Positioning System, Global
Orbiting Navigational Satellite System, Loran, Omega, Decca, Tacan, JTIDS
Relnav and Personal Location Reporting Service, where said LD means has an
LD signal antenna to receive said LD signals form said LD signal source
and has an LD signal receiver/processor to receive said LD signals from
the LD signal antenna and to determine the present location of the LD
signal antenna from said LD signals. |
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Claims |
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Description |
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FIELD OF THE INVENTION
This invention relates to monitoring adherence by a vehicle to a planned
route and schedule, using a location determination system.
BACKGROUND OF THE INVENTION
When a vehicle attempts to follow a planned route and schedule, it is often
appropriate to monitor adherence by the vehicle to the route and/or
schedule, especially if the vehicle is a common carrier, such as a public
transit bus or railway train. In such instance, the vehicle schedule is
often published, and some of the public relies on the schedule in planning
for its transportation needs. If the route or schedule is regularly
disrupted or modified substantially, monitoring route and schedule
adherence will identify the problem and perhaps provide a solution,
through modification of the published schedule and/or route.
Monitoring adherence to a route or schedule is not straightforward if the
vehicle can make, or not make, many stops or slight excursions in response
to the needs of its users. Some systems have been proposed for monitoring
the present and past locations of a vehicle. In U.S. Pat. No. 4,651,157,
Gray et al disclose a security monitoring and tracking system for a
terrestrial or marine vehicle that uses navigational information provided
an array of by a Loran-C or satellite-based signal transmitters. These
signals are received by a transceiver mounted on the vehicle and are
retransmitted to a central station for analysis and post-processing of the
signals, to determine the latitude and longitude of the vehicle at the
time the signals were originally received thereat.
Olsen et al, in U.S. Pat. No. 4,814,711, discloses a survey system for
collection of real time data from a plurality of survey vehicles, each of
which determines its present location using global positioning system
(GPS) signals received from a plurality of GPS satellites. A central
station periodically polls each survey vehicle and receives that survey
vehicle's present location coordinates by radio wave communication. The
central station compares that vehicle's path with a survey pattern
assigned to that vehicle. The geophysical or survey data measured by a
vehicle are also received by the central station and are coordinated with
that vehicle's location at the time were taken.
A vehicle tracking system, using an on-board Loran or GPS navigational
system, is disclosed in U.S. Pat. No. 5,014,206, issued to Scribner et al.
The vehicle receives Loran or GPS signals and determines its present
location coordinates but transmits these coordinates to a central station
only upon the occurrence of a specified event or events. This event might
be stopping of the vehicle for a time interval of length more than a
selected threshold or opening of the cargo doors or any other unusual
event.
Harker et al disclose a method for analyzing transportation schedules of a
transportation vehicle, such as a railway train or bus, to produce
optimized schedules, in U.S. Pat. No. 5,177,684. The method uses
information on the vehicle's assigned path and average speed and mobility
of the vehicle and determines a realistic, optimum schedule, including
arrival and departure times, that the vehicle can adhere to along that
path.
U.S. Pat. No. 5,191,341, issued to Gouard et al, discloses a tracking
system for a plurality of marine vessels, using two or more radio beacons
and a fixed or mobile central station. Each marine receives signals from
each beacon and relays these signals to the central station for
determination of the present location of the vessel, using standard
intersections of two or more hyperbolas for this purpose. A vessel's
present location is tracked for routing, entrance into and exit from a
harbor, arrival at and departure from a pier, and other similar purposes.
Navigation apparatus that stores location coordinates for a sequence of
intermediate or final destination points on a non-volatile memory, such as
a CD-ROM, is disclosed by Nimura et al in U.S. Pat. No. 5,231,584. A
vehicle or traveller activates the apparatus at a departure point, then
communicates its arrival at one or more designated intermediate or final
destination points by pressing a button at the time of arrival. The
apparatus does not track time of arrival and provides little direct
information on the present location of the vehicle or traveller between a
departure point and the next destination point.
Stanifer et al, in U.S. Pat. No. 5,243,530, disclose a system for tracking
a plurality of terrestrial, marine or airborne vehicles, using a local
area network and packet communication of location information. Loran-C
signals are received by a receiver/processor/transmitter on a vehicle, the
vehicle's present location is determined, and this location information is
transmitted to a central station, using LAN packet protocols,
acknowledgment signals and backoff/retransmission procedures that are
standard in the LAN art. If a given vehicle's present location is not
received by the central station within a time interval of selected length,
the central station requests transmission of the present location from
that vehicle.
A navigation system that provides off-route detection and route
re-optimization is disclosed in U.S. Pat. No. 5,262,775, issued to Tamai
et al. The system is mounted on a vehicle and uses GPS or Loran signals to
determine the present location of the vehicle. When the vehicle is
determined to be off-course, relative to its planned route, by more than a
selected threshold distance, the system notifies the vehicle operator of
this deviation and computes and displays a new optimized route, beginning
at the vehicle's present location.
In U.S. Pat. No. 5,272,638, Martin et al disclose a system for optimizing a
travel route for a vehicle, based on a shortest-path algorithm of Dijkstra
(which is neither explained nor referenced in the patent). The system uses
a roadway database, with distances between roadway decision points
included, and determines the order of destination points and the shortest
route to be followed by a vehicle, such as a truck making deliveries to a
plurality of destinations. The present location of the vehicle is not
tracked between intermediate destination points along the route.
A navigation system using audio communication between the system and an
operator of a vehicle is disclosed in U.S. Pat. No. 5,274,560, issued to
LaRue. The system is provided with a roadway database, a departure point
and a destination point. The system uses artificial intelligence
techniques to determine the optimum route to be followed, then
communicates with the vehicle operator to direct the vehicle along the
chosen route, unless overridden by voice command from the vehicle
operator. The present location of the vehicle is not tracked by an
independent ground-based or satellite-based location determination system
along the route.
What is needed is an approach that allows more focused monitoring of the
vehicle's present location, based on the present time and the route and
schedule nominally followed by the vehicle. Preferably, the frequency of
reporting of the location and time of observation should be relatively low
when the vehicle stays within its allocated ranges in space and time, and
this frequency should become appreciable only where the vehicle manifests
frequent or continuing above-threshold excursions relative to its planned
route and/or schedule. Preferably, the approach should allow use of other
location aids, such as a vehicle odometer, or use of other methods, such
as dead reckoning, to supplement and improve the accuracy of the location
and/or observation time determined by the monitoring system.
SUMMARY OF THE INVENTION
These needs are met by the invention, which provides methods for monitoring
the adherence of a vehicle to a planned route and/or planned time
schedule, within a selected corridor in location and time, where the
vehicle follows a selected route. The invention uses a ground-based or
satellite-based location determination (LD) system, such as GPS, GLONASS,
Loran-C, Omega, Decca, Tacan, JTIDS Relnav or PLRS, positioned on the
vehicle, to determine and store the present location of the vehicle. The
vehicle communicates its present location, route status (on-route or
off-route), schedule status (on-schedule, minutes ahead of schedule, or
minutes behind schedule), and other relevant information, to a central
station from time to time. The vehicle processor attempts to place the
vehicle at the correct point on or mean the route by correlating the route
and schedule data with the current time of day and current vehicle
geo-position. The time of day and schedule data are used to localize the
initial search. A snap-to-route command is provided to identify the
location on the assigned route that is closest to the vehicle's present
location as determined by the on-board LD system. If the present location
of the vehicle is not available from the on-board LD system, the invention
uses dead reckoning or route propagation to estimate the present location
of the vehicle. Dead reckoning integrates vehicle distance travelled
(computed from either the vehicle velocity vector or the odometer reading)
with the direction cosines of the vehicle's motion to estimate the current
position. Route propagation matches vehicle distance travelled, and
optionally the direction cosines of the vehicle's motion, against the
route and schedule data to achieve greater precision in estimating the
vehicle position than can be achieved by dead reckoning alone.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 illustrates an environment in which the invention can be used.
FIG. 2 illustrates time intervals associated with a time schedule S along a
path P, used in one embodiment of the invention.
FIG. 3 illustrates a method of using a snap-to-route command in another
embodiment of the invention.
FIGS. 4 and 5 are flow charts illustrating procedures suitable for
monitoring adherence to a selected route or to a selected time schedule
along that route.
FIGS. 6, 7, 8, 9, 10 are flow charts of procedures, according to the
invention, that can be used to determine spatial location coordinates and
velocity coordinates of a monitored vehicle with reference to a selected
route or time schedule, using snap-to-route and dead reckoning techniques.
DETAILED DESCRIPTION OF THE INVENTION
The invention can be used in an environment illustrated in FIG. 1, where a
vehicle 11 proceeds along a selected route R according to a selected or
predetermined schedule S. The selected route R is defined by a path P,
which may be continuous or may include two or more separated path
components, and a path is enclosed in a sequence of corridor segments
C.sub.k (k=1,2, . . . ). Each corridor segment C.sub.k surrounds a path
segment P.sub.k and is defined by and includes two or more boundaries
B.sub.k,1 and B.sub.k,2 that are spaced apart from that path segment by a
positive distance d.sub.k. The vehicle 11 is said to adhere to the route
over that path segment if the vehicle remains within the corridor segment
C.sub.k that surrounds and defines that path portion when the vehicle
moves along or adjacent to that path segment.
The selected schedule of the vehicle 11 may be defined by a discrete
sequence of pairs (TI.sub.n, L.sub.n), with each such pair containing a
location L.sub.n (n=1,2, . . . ) along the path P and a corresponding time
interval TI.sub.n, given by t.sub.n -.DELTA.t.sub.n
.ltoreq.t.ltoreq.t.sub.n +.DELTA.t.sub.n, with .DELTA.t.sub.n <0. It is
further required that t.sub.n -.DELTA.t.sub.n .ltoreq.t.sub.n+1
-.DELTA.t.sub.n+1, to provide a natural ordering of the time intervals
TI.sub.n. However, the constraint t.sub.n +.DELTA.t.sub.n
.ltoreq.t.sub.n+1 +.DELTA.t.sub.n+1 is not required.
The vehicle 11 is required to move through or adjacent to the location
L.sub.n at a time t within the time interval TI.sub.n. Adherence to a
(time) schedule does not, by itself, require that the vehicle move along
the path P, only that the vehicle pass through or near or adjacent to the
locations L.sub.n within the respective time intervals TI.sub.n. Adherence
to a route or path P does not, by itself, require that the vehicle pass
through any particular location, such as L.sub.n, on the vehicle's actual
path at any particular time. A vehicle may be monitored for adherence to a
selected route, for adherence to a selected time schedule, or for
adherence to a selected route and time schedule.
Assume that the vehicle 11 is being monitored for route and/or time
schedule adherence. The vehicle will carry a location determination (LD)
system 13 that includes an LD antenna 15, an LD receiver/processor 17, and
a computer 19 containing an electronic map including the path P to be
followed and/or the schedule S to be followed. Two or more consecutive
time intervals TI.sub.n may have a non-empty intersection (TI.sub.n
.OMEGA.TI.sub.n+1 .noteq..phi., the empty set) including one time value or
a range of time values in common, or this intersection may be empty, as
illustrated in FIG. 2. The LD antenna 15 receives LD signals from three or
more LD signal sources 21, 22, 23 and 24, which may be satellites or
ground-based signal towers. If the vehicle 11 does not adhere to the route
R, a transmitter 25 carried on the vehicle 11 transmits a route deviation
signal, which may include the (first) location L.sub.d where route
non-adherence occurred, to a receiver 26 at a central station 27 that
collects such data (FIG. 1).
The path P may be approximated as a sequence {P.sub.n }.sub.n of linear
segments/brining a connected curve, where the intersection of two
consecutive path segments P.sub.n and P.sub.n+1 is a point or connected
continuum of points on or near the actual path P. If the vehicle 11
follows a time schedule S for the path P, the vehicle need only be near
the specified location L.sub.n for at least one time t within the time
interval TI.sub.n. Otherwise stated, it is only required that, for at
least one time point t' in the time interval TI.sub.n, a vehicle present
location L(t') be found at that time that is near the specified location
L.sub.n. If non-adherence to the time schedule S occurs, the vehicle
transmitter 25 notifies the central station 27 and may include the
specified location L.sub.d where schedule non-adherence (first) occurred.
FIG. 3 indicates a snap-to-route (SR) technique for locating a
time-scheduled vehicle 11 by reference to the path P to be followed by
that vehicle. Again, the path P is approximated by a sequence of linear
segments {P.sub.n }.sub.n, where two consecutive segments have a non-zero
intersection. At any time t, the time-scheduled vehicle 11 is determined
by the LD system to have a location L that may or may not lie on any of
the line segments P.sub.n. Assume the vehicle location L has
three-dimensional Cartesian coordinates (x(L), y(L), z(L)). Express the
locus of points on a line segment P.sub.n in normal form as
x cos .theta..sub.x,n +y cos .theta..sub.y,n +z cos .theta..sub.z,n
=P.sub.n, (1)
where cos .theta..sub.x,n, cos .theta..sub.y,n and cos .theta..sub.z,n are
the direction cosines of the normal to a plane containing the line segment
P.sub.n and P.sub.n is the perpendicular distance from the coordinate
origin to this plane. If the change in the vertical coordinate z along any
path segment P.sub.n is ignored here (equivalent to setting cos
.theta..sub.z,n =0), Eq. (1) simplifies to
x sin .theta..sub.n +y cos .theta..sub.n =P.sub.n, (2)
where .theta..sub.n is the angle that the line segment P.sub.n makes with
the x-axis of the chosen coordinate system and d.sub.n is the length of
the line drawn through the origin and perpendicular to the line segment
P.sub.n, as illustrated in FIG. 3. Equations (1) and (2) are derived by W.
A. Wilson and J. I. Tracey, Analytic Geometry, D. C. Heath and Co., 1949,
pages 63-64, 68, 266-269, incorporated by reference herein.
For each integer n=1, 2, . . . , the system computes a distance D.sub.n
from the relation
x(L) cos .theta..sub.x,n +y(L) cos .theta..sub.y,n +z(L) cos
.theta..sub.z,n -P.sub.n =-D.sub.n (L). (3)
The two-dimensional version of Eq. (3) becomes
x(L) sin .theta..sub.n +y(L) cos .theta..sub.n -P.sub.n =-D.sub.n (L).(4)
The system then determines the integer n=N for which D.sub.n (L) is
minimized and displays the location of the perpendicular foot .pi..sub.N
(L) of the vehicle location (x(L), y(L), z(L) ) on the line segment
P.sub.N, as illustrated in FIG. 3. As used here, the "perpendicular foot"0
.pi..sub.n (L) is a point on a line segment P.sub.n that is closest to the
vehicle location L. The LD system may have a snap-to-route command that,
for any vehicle location (x(L), y(L), z(L)), displays the location
.pi..sub.N (L) on the "closest" line segment P.sub.N that approximates
part of the route R or path P to be followed by the vehicle 11.
Optionally, the system can also display the distance D.sub.N (L) for the
footer .pi..sub.N (L).
If two or more of the distances, say, D.sub.N' (L) and D.sub.N" (L), each
achieve the minimum value among these distances, each corresponding
perpendicular foot .pi..sub.N' (L) and .pi..sub.N" (L) can be displayed on
the map. Alternatively, one of these perpendicular feet .pi..sub.N' (L)
and .pi..sub.N" (L) can be chosen for display and/or further use, based
upon an algorithm that compares the present velocity components
(v.sub.x,N, v.sub.y,N, v.sub.z,N) of the vehicle with the direction
components (cos .alpha..sub.x,n, cos .alpha..sub.y,n, cos .alpha..sub.z,n)
of a tangent line drawn to each of the path segments P.sub.N' and
P.sub.N" at the respective locations .pi..sub.N' and .pi..sub.N" on
these path segments. The perpendicular foot .pi..sub.N (L) (N=N' or N")
would be chosen for which the local tangent line components of the path
segment provide the best match for the present velocity components. That
is, the quantity
.DELTA.v.sub.N =[(v.sub.x,n -v.sub.N cos .alpha..sub.x,N).sup.2 +(v.sub.y,n
-v.sub.N cos .alpha..sub.y,N).sup.2 +(v.sub.z,n -v.sub.N cos
.alpha..sub.z,N).sup.2 ].sup.1/2, (5)
is minimized by the choice of N=N' or N=N", where
v.sub.N =[v.sub.x,N.sup.2 +v.sub.y,N.sup.2 +v.sub.z,N.sup.2 ].sup.1/2(6)
is the magnitude of the present velocity of the vehicle.
At times the LD system may be unable to provide an estimated location for
the vehicle 11 of interest, because of signal interference by an
electromagnetic disturbance in the troposphere or ionosphere, because of
shadowing by an opaque or partly opaque structure that is located between
the moving vehicle and a source of LD signals, or for other reasons. In
such situations, a dead reckoning (DR) approach can be used to estimate
the present location of the vehicle 11, assuming that the velocity
components (or the acceleration components) of the vehicle remain
unchanged over the time interval for which DR approximation is used.
Assume that the last vehicle location provided by the LD system had the
location coordinates (x(t.sub.1), y(t.sub.1), z(t.sub.1)), with t.sub.1
=t.sub.L -.DELTA.t<t.sub.L, before the location signals were lost. Using
an average velocity vector (v.sub.x,avg, v.sub.y,avg, v.sub.z,avg) of the
vehicle (found from comparison of location coordinates for times up to and
including t=t.sub.1) and assuming that the vehicle acceleration components
are zero, the vehicle's predicted progress along or parallel to the
sequence of line segments P.sub.n is estimated or extrapolated to provide
an extrapolated location for t>t.sub.1 for the vehicle, with location
coordinates approximately given by
x(t)=x(t.sub.1)+v.sub.x,avg (t--t.sub.1) (.DELTA.t.sub.1), (7)
y(t)=y(t.sub.1)+v.sub.y,avg (t--t.sub.1), (8)
z(t)=z(t.sub.1)+v.sub.z,avg (t--t.sub.1). (9)
If the average acceleration components (a.sub.x,avg, a.sub.y,avg,
a.sub.z,avg) of the vehicle for times preceding the time t=t.sub.1
=t.sub.L -.DELTA.t are also taken into account, Eqs. (7), (8) and (9) are
replaced by the relations
x(t)=x(t.sub.1)+v.sub.x,avg (t--t.sub.1)+a.sub.x,avg (t--t.sub.1).sup.2 /2
(t.gtoreq.t.sub.1), (10)
y(t)=y(t.sub.1)+v.sub.y,avg (t--t.sub.1)+a.sub.y,avg (t--t.sub.1).sup.2
/2,(11)
z(t)=z(t.sub.1)+v.sub.z,avg (t--t.sub.1)+a.sub.z,avg (t--t.sub.1).sup.2
/2.(12)
As in the preceding development, the vertical coordinate (z) Equations (9)
and/or (12) can be deleted if substantially all vehicle motion takes place
approximately in a plane. This DR extrapolation can be used to estimate
the vehicle's present location for short time intervals when the LD system
cannot provide accurate location coordinates.
Alternatively, an odometer or other distance measuring device can be
mounted on the vehicle to determine the accumulated distance .delta.(t)
moved by the vehicle at any time t. If signals from the LD system are lost
after a time t=t.sub.1 =t.sub.L -.DELTA.t, the present location
coordinates of the vehicle are then determined approximately by the
relations
x(t)=x(t.sub.1)+[.delta.(t)-.delta.(t.sub.1)] cos .theta..sub.vx,avg
(t.gtoreq.t.sub.1), (13)
y(t)=y(t.sub.1)+[.delta.(t)-.delta.(t.sub.1)] cos .theta..sub.vy,avg,(14)
z(t)=z(t.sub.1)+[.delta.(t)-.delta.(t.sub.1)] cos .theta..sub.vz,avg.(15)
Here (cos .theta..sub.vx,avg, cos .theta..sub.vy,avg, cos
.theta..sub.vz,avg) are the average velocity direction cosines of the
vehicle for time t.ltoreq.t.sub.L -.DELTA.t and are defined by the vehicle
average velocity components
cos .theta..sub.vx,avg =v.sub.x,avg /[v.sub.x,avg.sup.2 +v.sub.y,avg.sup.2
+v.sub.z,avg.sup.2 ].sup.1/2, (16)
cos .theta..sub.vy,avg =v.sub.y,avg /[v.sub.x,avg.sup.2 +v.sub.y,avg.sup.2
+v.sub.z,avg.sup.2 ].sup.1/2, (17)
cos .theta..sub.vz,avg =v.sub.z,avg /[v.sub.x,avg.sup.2 +v.sub.y,avg.sup.2
+v.sub.z,avg.sup.2 ].sup.1/2, (18)
for some interval of times t.ltoreq.t.sub.1. This alternative has the
advantage that the vehicle's actual speed for times t>t.sub.1 are
accounted for by use of the odometer distance .delta.(t).
As a second alternative for dead reckoning, the vehicle can use an on-board
magnetometer or other device that senses the present direction that the
vehicle is travelling, plus a speedometer or other velocity monitor that
determines the vehicle speed v(t), to estimate the present location
coordinates of the vehicle by the relations
##EQU1##
One problem often encountered with use of dead reckoning is that the
vehicle heading, given by the velocity direction cosine coordinates (cos
.theta..sub.vx, cos .theta..sub.vy, cos .theta..sub.vz), drifts with
passage of time. The dead reckoning and snap-to-route techniques can be
combined to provide periodic recalibration of the heading or direction
cosine coordinates, by adjusting the estimated heading coordinates by the
local direction cosines of the path segment P.sub.N at the snap-to-route
location of the perpendicular footer .pi..sub.N. The snap-to-route
direction cosines at the perpendicular footer location .pi..sub.N and/or
the spatial location coordinates of the perpendicular footer .pi..sub.N
can be substituted for the corresponding values that are presently
estimated using DR. The time interval for recalibration of these DR
estimates is determined by the estimated drift in the heading coordinates;
the time interval length for recalibration decreases as the maximum drift
rate increases.
Alternatively, each DR-determined estimate of vehicle location coordinates
and/or vehicle heading coordinates can be replaced by the corresponding
location coordinates and/or heading coordinates determined using the SR
technique. Here, DR is used to estimate the location and heading
coordinates, and these estimates are automatically replaced by the
location and heading coordinates determined using SR to identify a path
segment P.sub.N and perpendicular footer .pi..sub.N on this path segment.
FIGS. 4 and 5 illustrate suitable procedures for monitoring adherence by a
vehicle to a selected route R and to a selected time schedule along the
route R, respectively. In step 31 of FIG. 4, a location determination (LD)
means carried by the vehicle determines the present location L of the
vehicle at a sequence of one or more discrete times. In step 33, an
electronic map connected to the LD means represents a selected route R as
a sequence of path segments P.sub.k, with each such path segment being
surrounded by a segment corridor C.sub.k of selected, positive, transverse
width 2d.sub.k. In steps 35 and 37, the system determines a perpendicular
footer .pi..sub.k (L) of the location L, if it exists, on each of the path
segments P.sub.k and determines whether, for at least one value of the
index k, the distance D.sub.k (L) satisfies
D.sub.k (L).ltoreq.d.sub.k. (22)
If Eq. (12) is satisfied for at least one value of the index k, the vehicle
is determined to be adhering to the selected route R at the vehicle
location L (step 38). Otherwise, the vehicle is determined to be not
adhering to the selected route R at the vehicle location L (step 39).
After step 38 or step 39, the system recycles and considers another path
segment P.sub.k or another segment corridor C.sub.k, if any.
In step 41 of FIG. 5, the system represents a selected tome schedule as an
ordered sequence of one or more triples {(TI.sub.m,L.sub.m,d.sub.m
}.sub.m, where TI.sub.m ={t.vertline.t.sub.m -.DELTA.t.sub.m
.ltoreq.t.ltoreq.t.sub.m +.DELTA.t.sub.m } is a time interval positive
length 2.DELTA.t.sub.m, L.sub.m is a selected location (specified by
location coordinates) in a region through which the vehicle passes, and
d.sub.m is a selected positive distance. In step 43, a location
determination (LD) means carried by the vehicle determines the present
location L(t'.sub.r,u) (u=1,2,. . . ) of the vehicle at a sequence of one
or more discrete times t'.sub.r,u in at least one of the time intervals
TI.sub.r. In step 45, the system determines whether at least one of the
locations L(t'.sub.r,u) determined in the time interval TI.sub.r is
sufficiently close to the prescribed location L.sub.r in that time
interval; that is, whether
distance .vertline.L(t'.sub.r,u)-L.sub.r .vertline..ltoreq.d.sub.r.(23)
If the answer is "yes", the system determines in step 47 that the vehicle
is adhering to the time schedule in the time interval TI.sub.r. If the
answer is "no", the system determines in step 48 that the vehicle is not
adhering to the time schedule in the time interval 48. After step 48, the
system optionally notifies the central station that the vehicle has not
adhered to the time schedule in the time interval TI.sub.r and/or of the
location L.sub.r where time schedule non-adherence has occurred. After
step 47 or step 48, the system recycles and considers a new time schedule
triple (TI.sub.m,L.sub.m,d.sub.m) (m.noteq.r), if any.
FIGS. 6, 7, 8, 9 and 10 illustrate suitable procedures for determining the
spatial location coordinates and/or the heading coordinates for a vehicle,
using SR, using DR, and using SR and DR combined, respectively. In step 51
of FIG. 6, a location determination (LD) means carried by the vehicle
determines the present location L of the vehicle at a sequence of one or
more discrete times f.sub.k. In step 53, an electronic map connected to
the LD means represents a selected route R as an ordered sequence of path
segments P.sub.k. In step 55, the system computes the location of the
perpendicular foot .pi..sub.k for the location L on one or more path
segments P.sub.k. In step 57, the system determines the distances D.sub.k
(L) of each perpendicular foot .pi..sub.k (L) from the location L and
determines the index k=K with the minimum distance D.sub.k (L). In step
59, the system selects the location .pi..sub.K (L) as the SR vehicle
location on the route R. In step 61 (optional), the system displays this
selected SR location .pi..sub.K (L) numerically in terms of its location
coordinates and/or graphically on a map. In step 63 (optional), the system
determines or estimates the direction cosines for the path segment P.sub.K
at the location of the perpendicular foot .pi..sub.K (L).
In step 71 of FIG. 7, the system determines average velocity components
(v.sub.x,avg, v.sub.y,avg, v.sub.z,avg) and/or average acceleration
components (a.sub.x,avg, a.sub.y,avg, a.sub.z,avg) for the vehicle up to
and including a time t'=t.sub.1 =t.sub.L -.DELTA.t. In step 73, a location
determination (LD) means carried by the vehicle. In step 75, the system
estimates the DR-based present location coordinates of the vehicle for a
time t>t.sub.1 using the relations
x(t)=x(t.sub.1)+v.sub.x,avg (t--t.sub.1)+a.sub.x,avg (t--t.sub.1).sup.2
/2,(10)
y(t)=y(t.sub.1)+v.sub.y,avg (t--t.sub.1)+a.sub.y,avg (t--t.sub.1).sup.2
/2,(11)
z(t)=z(t.sub.1)+v.sub.z,avg (t--t.sub.1)+a.sub.z,avg (t--t.sub.1).sup.2
/2.(12)
discussed above for t>t.sub.1. As in | | |
