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Description  |
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BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a navigation system using an angular rate
sensor, and more specifically to a navigation system by which automotive
vehicle travel locations are detected by an angular rate sensor and a
distance sensor and the detected vehicle locations are projected on a
displayed map road, so that the vehicle travel display moves along a
predetermined route on the map.
Since this system can operate independently without the need of other
auxiliary means (e.g. radio signals), this system is effective in an an
area where radio navigation systems cannot operate reliably, such as an
urban area or other areas subject to radio interference.
2. Description of the Prior Art
The applicant has already proposed a dead reckoning and map correlation
system for automotive vehicle tracking, which uses an angular rate sensor
and a distance sensor, in Japanese Unexamined Published (Kokai) Patent
Application No. 60-48600, entitled Vehicle Position Detecting System. In
this system, current vehicle locations can be intermittently detected on
the basis of vehicle travel distance data and vehicle travel angle data
((detected by an angular rate (velocity) sensor)); and the calculated
vehicle locations are projected onto the roads displayed on a digital map
(including road intersections and curves) previously prepared by inputting
digital map data to a CPU through a keyboard so that the vehicle travel
motion can track a road displayed on the map.
In the navigation system of this kind, it is extremely difficult to correct
the error between the current location and the map road, so that the
displayed vehicle motion can correctly track a predetermined road on the
digital map. The correction method of the above-mentioned prior-art system
will be described with reference the attached drawings. In FIG. 1(A),
P'(X, Y) denotes coordinates of the current detected vehicle location
point (not displayed); P.sub.1 (X.sub.1, Y.sub.1) denotes coordinates of
an intersection of roads; S.sub.1 denotes a distance between the detected
vehicle location data P' and the intersection data P.sub.1 ; .theta.
denotes an angle data subtended by the two lines P.sub.1 P' and P.sub.1
P.sub.01. Further, the dashed curve denotes an actual vehicle travel route
(not displayed).
The above distance data S.sub.1 and the angle data .theta. are detected for
each predetermined distance to obtain the current detected vehicle
location P'(X, Y). In FIG. 1(A), since the calculated position P' deviates
from the route R, this position P' is projected on the route R for
correction. That is, a corrected vehicle location P.sub.01 (X.sub.01,
Y.sub.01) is calculated in accordance with the following expression:
X.sub.01 =X.sub.1 +S.sub.1 cos .theta.
Y.sub.01 =Y.sub.1 +S.sub.1 sin .theta.
S.sub.1 =.sqroot.(X.sub.1 -X).sup.2 +(Y.sub.1 +Y).sup.2
The above-mentioned correction method is fairly effective when the vehicle
travels along a straight road. However, when the vehicle turns along an
intersection or a curved road, various problems arise as follows:
(1) 1st problem
In this method, it is possible to reduce a correction error at an
intersection as shown in FIG. 1(B). In more detail, even if the vehicle
turns at an intersection as shown by dashed lines, since the distance
D.sub.e can automatically be corrected at the intersection, the correction
error between the actual and corrected points is small.
However, when the vehicle travels along an inflection as shown by dashed
lines in FIG. 1(C), since D.sub.e cannot be corrected, there exists a
large error e.
(2) 2nd problem
In this system, a route judge area as shown in FIG. 2(A) is determined at
each branch point P.sub.1 to determine a turning point for the vehicle.
That is, when a distance L.sub.1 between the current vehicle location
P.sub.00 and the succeeding branch point P.sub.1 becomes less than a
predetermined value L.sub.1, since this indicates that the vehicle
approaches a branch point P.sub.1, a revised distance calculation begins
to detect that the vehicle has passed through the point P.sub.1. And, when
the calculated distance exceeds a predetermined value (L.sub.1 +L.sub.2),
it is determined that the vehicle has turned at the branch point P.sub.1
by detecting the travel angle.
In the prior-art method, however, since this route judge area (L.sub.1
+L.sub.2) is fixed, when an adjacent point P.sub.2 is close to the point
P.sub.1, there exists a problem in that the vehicle passes beyond the
adjacent point P.sub.2 before the vehicle turns at the point P.sub.1, thus
resulting in route change judgement error. Further, there exists another
problem in that it is impossible to determine a sufficient route judgement
distance between the two points P.sub.1 and P.sub.2.
Further, there exists another problem in that when a distance between two
points P.sub.1 and P.sub.s is long and a large error occurs, the
calculated distance to the point is quite different from an actual
distance, so that it is impossible to detect a route judge area when the
vehicle has passed through the point. The above-mentioned error between
the calculated map distance and the actual distance is produced when a
curved road R is approximated by a straight line P.sub.1 P.sub.2 as shown
in FIG. 2(B). That is, the curved actual distance is larger than the
straight map distance when the vehicle travels from P.sub.1 to P.sub.2,
and shorter than the straight map distance when the vehicle travels from
P.sub.2 to P.sub.1. Therefore, where these road inflections continue as
shown in FIG. 2(C), there exists a problem such that cumulative errors are
produced.
When the above error is produced, since there exists a difference in
distance between the map branch point and the actual branch point, it is
impossible to detect route change data within a route judge area JE.
FIG. 2(D) shows an example where the vehicle turns at the actual branch
point B.sub.A before the route judge area JE of the map branch point
B.sub.M is detected, because the distance between two map branch points is
longer than the actual distance. FIG. 2(E) shows an example where the
vehicle turns at the actual branch point B.sub.A after the vehicle has
passed through the route judge area JE of the map branch point B.sub.M,
because the distance between two map branch points is shorter than the
actual distance.
(3) 3rd problem
In this system, straight routes between two points (e.g. intersections,
branch points, turning corners, etc.) are calculated on the basis of map
data including coordinates of these points and point numbers adjacent to
each point, and the current vehicle travel locations are displayed along
these calculated straight routes. Further, in order to judge a change in
vehicle travel direction, a route judge area JE is provided at each point
P.sub.1 as shown in FIGS. 3(A) and 3(B).
The third problem is how to display the current vehicle location within
this route judge area JE.
In the prior-art system, the current vehicle location is continuously
displayed along the route on which the vehicle runs toward the point
P.sub.1, as shown by white dots in FIG. 3(A) or fixedly displayed at the
point P.sub.1 as shown by a black dot in FIG. 3(B).
Therefore, in the case shown in FIG. 3(A), since the vehicle location is
displayed even on an extension of the route P.sub.0 P.sub.1, there exists
a problem in that a location mark is dislocated from the route when the
vehicle turns at a T-shaped crossing or displayed as if the vehicle
travels straight in spite of the fact that the vehicle turns right or left
at a crossroads, thus resulting in a display error.
Further, in the case shown in FIG. 3(B), since the display mark jumps from
the point P.sub.1 to a corrected location after a route change has been
determined, there exists another problem in that the location is displayed
in an unnaturally appearing manner.
SUMMARY OF THE INVENTION
With these problems in mind, therefore, it is the general objective of the
present invention to provide a navigation system using an angular rate
sensor which can accurately display the current vehicle travel location on
a map by minimizing display errors.
More specifically, it is a first object of the present invention to provide
a navigation system which can eliminate a display error caused at each
branch point.
It is a second object of the present invention to provide a navigation
system which can reliably determine area judge values so as to provide an
indication that the vehicle has reached and passed through a route judge
area even if a distance between two adjacent points is short or when the
vehicle turns a corner gently.
It is a third object of the present invention to provide a navigation
system which can reliably determine a area judge value so as to provide an
indication that the vehicle has entered into a route judge area even if
there exists a long curved road on the map.
It is a fourth object of the present invention to provide a navigation
system which can display the vehicle location in a naturally appearing
manner at each branch point even within the route judge.
To achieve the above-mentioned object, the navigation system for displaying
travel locations of a vehicle on a displayed map, according to the present
invention comprises: (a) means for detecting vehicle travel angle; (b)
means for detecting vehicle travel distance; (c) means, coupled to said
vehicle travel angle detecting means and said vehicle travel distance
detecting means, for calculating vehicle locations on the basis of
detected vehicle travel angles and distances; (d) means for storing map
information data including branch points; (e) means, coupled to said map
information data storing means, for setting a route judge area at each
branch point to determine a route along which the vehicle travels at a
branch point; (f) means, coupled to said vehicle distance detecting means,
said map storing means and said route judge area setting means, for
determining the condition of a vehicle passing into the set route judge
area when a distance between a current vehicle location and a succeeding
branch point becomes shorter than a predetermined value and the condition
of a vehicle passing through the set route judge area when a distance
between a position at which vehicle passing into the set route judge area
is determined and a current vehicle location becomes longer than a
predetermined value; (g) means, coupled to said vehicle travel angle
detecting means and said route judge area pass determining means, for
determining travel route at each branch point by comparing a travel angle
detected by said travel angle detecting means with map data stored in said
map data storing means when the vehicle has passed through the set route
judge area; (h) means, coupled to said vehicle location calculating means
and said travel route determining means, for correcting calculated vehicle
locations so as to be located along a road on a displayed map, said
vehicle location calculating means further correcting a vehicle after-turn
location at each branch point by matching a vehicle turn point obtained
when said route judge area pass determining means detects that the vehicle
has passed through a route judge area to a map branch point within the
route judge area; and (i) means, coupled to said correcting means, for
displaying a map stored in said map information data storing means and
vehicle locations corrected by said correcting means.
The route judge area setting means sets an area pass judge value to detect
a route judge area adjustably according to route conditions to an adjacent
branch point or increases a route judge area by increasing the area pass
judge value when the vehicle travel angle detecting means detects a travel
angle beyond a predetermined value.
Further, the route judge area setting means sets an area pass judge value
to detect a route judge area by integrating plural area judge values
between two adjacent points within a curved road.
Further, vehicle locations are displayed without correction only within the
route area judge area.
In summary, to achieve the first object, when the vehicle has passed
through a branch point, the current vehicle location is corrected to the
map branch point.
To achieve the second object, an area pass judge value for determining that
the vehicle has passed through a route judge area is adjustably determined
according to adjacent route conditions and increased when vehicle travel
angle exceeds a predetermined angle to prevent an error such that travel
route change is determined before the vehicle has actually turned a branch
point corner.
To achieve the third object, plural area judge values between two adjacent
points within a curved road are integrated.
To achieve the fourth object, vehicle travel locations are displayed on the
basis of non-corrected vehicle locations within each route judge area.
BRIEF DESCRIPTION OF THE DRAWINGS
The features and advantages of the navigation system using an angular rate
sensor according to the present invention will be more clearly appreciated
from the following description of the preferred embodiment of the
invention taken in conjunction with the accompanying drawings in which
like reference symbols designate the same or similar elements or sections
throughout the figures thereof and in which:
FIG. 1(A) is a diagram for assistance in explaining display correction of a
prior-art navigation system;
FIG. 1(B) is a diagram for assistance in explaining display correction at
an intersection of the prior-art navigation system;
FIG. 1(C) is a diagram for assistance in explaining an error produced at a
turning corner of the prior-art navigation system;
FIG. 2(A) is a diagram for assistance in explaining a fixed route judge
area of the prior-art navigation system;
FIG. 2(B) is a diagram for assistance in explaining an error between an
actual curved route and a straight route;
FIG. 2(C) is a diagram for assistance in explaining a cumulative error
produced in a curved road;
FIG. 2(D) is a diagram showing an erroneous operation involved in the
prior-art navigation system;
FIG. 2(E) is a diagram showing another erroneous operation involved in the
prior-art navigation system;
FIG. 3(A) is a diagram for assistance in explaining a non-natural display
involved in the prior-art navigation system;
FIG. 3(B) is a diagram for assistance in explaining another non-natural
display involved in the prior-art navigation system;
FIG. 4 is a basic block diagram of the navigation system of the present
invention;
FIG. 5 is an actual block diagram of the navigation system of the present
invention;
FIG. 6 is a diagram for assistance in explaining the correction operation
of the navigation system of the present invention;
FIG. 7 is a flowchart for assistance in explaining the operation of the
navigation system of the present invention;
FIG. 8 is a flowchart showing a subroutine of block S.sub.4 shown in FIG.
7;
FIG. 9 is a flowchart showing a subroutine of block S.sub.6 shown in FIG.
7;
FIG. 10 is another diagram for assistance in explaining a first feature of
the present invention, in which actual vehicle location (x.sub.n, y.sub.n)
is corrected to (X.sub.01, Y.sub.01) at a branch point P.sub.1 ;
FIG. 11 is a diagram for assistance in explaining the route judgement
operation of the navigation system of the present invention;
FIGS. 12(A), (B) and (C) are diagrams for assistance in explaining a second
feature of the present invention, in which the area pass judge value is
adjustable;
FIG. 13(A) is a diagram for assistance in explaining a third feature of the
present invention, in which an area judge value is determined by adding
each area judge value for each straight line within a curved road;
FIG. 13(B) is a diagram for assistance in explaining a method of displaying
a vehicle location at a turning corner; and
FIG. 14 is a diagram for assistance in explaining a fourth feature of the
present invention, in which non-corrected locations are displayed within a
route judge area.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
With reference to the attached drawings, a basic configuration of the
navigation system using angular rate sensor will be described hereinbelow
in more detail.
FIG. 4 shows a schematic block diagram showing a basic configuration of an
embodiment of the system according to the present invention. In FIG. 4,
the navigation system comprises travel angle detecting means A for
detecting a travel angle (.theta.=.intg.wdt) of an automotive vehicle on
the basis of a signal W from an angular rate sensor; travel distance
detecting means B for detecting a travel distance of the vehicle; location
calculating means C for calculating a current vehicle location on the
basis of the signals from the travel angle detecting means and the travel
distance detecting means; map memory means D for storing survey map data
including various point coordinates of intersections, branches and
inflections of roads; route judge area setting means E for setting a route
judge area at each branch point to determine a route along which the
vehicle travels at a branch point; route judge area pass determining means
F for determining that a vehicle passes into a set route judge area when a
distance between a current vehicle location and a succeeding branch point
becomes shorter than a predetermined value and for determining that a
vehicle passes through the set route judge area when a distance between a
position at which vehicle passing into the set route judge area is
determined and a current vehicle location becomes longer than a
predetermined value; travel route determining means G for determining a
vehicle travel route by comparing a travel angle detected by the travel
angle detecting means with map data stored in the map data storing means
when the vehicle has passed through the set route judge area; location
correcting means I for correcting the calculated vehicle location on the
judged map route; and displaying means for displaying the corrected
vehicle location on the map.
FIG. 5 shows a block diagram of the system of the present invention. In the
drawing, the system comprises a travel distance sensor 11 for generating a
signal indicative of the vehicle distance; an angular rate sensor 12 such
as a vibrating gyrosensor for detecting vehicle angular velocity; and a
CPU 13 for receiving signals outputted from the travel distance sensor 11
and the angular rate sensor 12. The CPU 13 operates in accordance with
programs stored in a ROM 14 to execute various operations by reading
various data from the RAM 15 and writing the processed data in the RAM 15.
Further, the CPU 13 is connected to a keyboard 16 for entering data, a
display unit such as CRT, and a memory 18 for storing survey map
information data.
FIG. 6 shows a diagram for assistance in explaining the map correction
method of the present invention. A point P(x, y) 1 is first initialized to
P.sub.00 (X.sub.00, Y.sub.00). An actual travel route 2 shown by dashed
line is calculated by the distance sensor and the angular rate sensor, and
compared with map data R.sub.0. As a result, vehicle locations are
displayed on a map on a CRT screen using symbols. The broken line 2 is a
route detected by the sensors and projected to the map route R for
correction and this is not displayed on the CRT map. Data for the
displayed map are prepared based on a survey map including intersections
or inflections of roads (referred to as points and straight lines). The
portion between two points is approximate by a straight line. The map is
digitally coordinated for each point and stored in the ROM.
In order to remove errors due to the straight line approximation of the
map, a certain range referred to as "route judge area JE" is set up at
each point at the rate proportional to the distance between two points
P.sub.0 and P.sub.1. In this area JE, judgement of a change in vehicle
travel direction and correction of errors are implemented. Within the area
judge area, the route or location calculated by the distance sensor and
the angular rate sensor is displayed without coordinate correction to the
map. However, when the vehicle passes out of the area judge area, the
symbol indicating the vehicle location is displayed along the map after
correction.
The map data stored in the memory 18 are position data expressed by X-Y
coordinates of branch points such as intersections, inflections of roads
as shown in FIG. 6 and includes the number of the points and the numbers
of other points adjacent thereto.
In more detail, the position data of a route as shown in FIG. 6 are as
follows:
______________________________________
Flag
Point No. X Y Adjacent point Nos.
(P)
______________________________________
P.sub.0 X.sub.0
Y.sub.0 P.sub.1, P.sub.4
1
P.sub.1 X.sub.1
Y.sub.1 P.sub.0, P.sub.1, P.sub.3
1
P.sub.2 X.sub.2
Y.sub.2 P.sub.1 0
P.sub.3 X.sub.3
Y.sub.3 P.sub.1 0
: : : :
: : : :
: : : :
P.sub.n
______________________________________
In the table, the coordinates of the point P.sub.0 are (X.sub.0, Y.sub.0)
and the adjacent points thereof are P.sub.1 and P.sub.4. The coordinates
of the point P.sub.1 are (X.sub.1, Y.sub.1) and the adjacent points
thereof are P.sub.0, P.sub.1 and P.sub.3 and so on.
Further, in this table, information data related to the adjacent point is
stored in the form of flag P. For instance, if flag is 1 at P.sub.0, this
indicates that there exists a special point to the adjacent point P.sub.1
or P.sub.4. The special point is a place having a very short distance to
the adjacent point, so that the ordinary route judgement processing is
disabled.
The operation of the system will be explained in accordance with a
flowchart shown in FIGS. 7 to 9 by taking an example where a vehicle
travels from a point P.sub.00 (X.sub.00, Y.sub.00) to a point P.sub.1
(X.sub.1, Y.sub.1) along a route R.sub.0 connecting two points P.sub.0
(X.sub.0, Y.sub.0) and P.sub.1 (X.sub.1, Y.sub.1) on a map shown in FIG.
6. Further, in FIG. 6, the dashed lines indicate calculated vehicle route
(not displayed).
The initial location P.sub.00 (X.sub.00, Y.sub.00) and two points P.sub.0
(X.sub.0, Y.sub.0) and P.sub.1 (X.sub.1, Y.sub.1) along a route R.sub.0
are entered through the keyboard 16 and stored in the RAM 15 for
initialization (in step S.sub.1). The entered current position and map
data including roads and place names are displayed (in step S.sub.2). In
this step S.sub.2, the current vehicle location P(x, y) is corrected on
the route R.
A gradient .theta..sub.0 of the route R.sub.0 with respect to a base line
L.sub.H (positive in the counterclockwise direction) is calculated on the
basis of two points P.sub.0 (X.sub.0, Y.sub.0) and P.sub.1 (X.sub.1,
Y.sub.2) as follows:
.theta..sub.0 =tan.sup.-1 .vertline.(Y.sub.0 -Y.sub.1)/(X.sub.0
`X.sub.1).vertline.
In the same way, gradients .theta..sub.2 and .theta..sub.3 with respect to
the base line L.sub.H are calculated on the basis of the two adjacent
points P.sub.1, P.sub.2, and P.sub.3 (in step S.sub.3).
In the succeeding step, a distance L.sub.n between P.sub.00 and P.sub.1 is
calculated as follows (in step S.sub.4):
L.sub.n =.sqroot.(X.sub.1 -X.sub.00).sup.2 +(Y.sub.1 +Y.sub.00).sup.2
Thereafter, an area judge value L.sub.c and an area pass judge value MM are
determined in accordance with a flowchart shown in FIG. 8 in order to set
a route judge area JE (in step S.sub.4).
Flags P are read from map data (in step S.sub.41) and control determines
whether the read flag is 1 (in step S.sub.42). If YES, control sets the
succeeding route flag P to 1 (in step S.sub.43) and sets b to 10 m, for
instance (in step S.sub.44). On the other hand, if NO in step (S.sub.42),
control sets the succeeding route flag P to 0 (in step S.sub.45) and sets
b to 20 m, for instance (in step S.sub.46). By doing this, the distance of
the route judge area (area pass judge value) can be adjusted according to
the succeeding route condition indicated by the flag P.
The standard distance (radius) L.sub.s of the area JE is calculated as
L.sub.n x a (in step S.sub.47), where L.sub.n denotes a distance to the
branch point P.sub.1 and a denotes 0.1, for instance, if 10% of the
distance L.sub.n is determined as the standard distance L.sub.s.
Control checks the number of branch points (routes) (in step S.sub.48). If
NO (an inflection of a road), control calculates an integrated standard
value L.sub.ss by integrating each standard value L.sub.s (in step
S.sub.49) along a curved road. This integrating calculation is
continuously made until control determines an intersection in step
S.sub.48 and control proceeds to the step S.sub.52.
After step S.sub.49, an area judge value (distance) L.sub.c is set to the
standard value L.sub.s (in step S.sub.50) and an area pass judge value MM
is set to L.sub.c +b (in step S.sub.51). In step S.sub.51, b is a constant
(e.g. 20 m) indicative of distance surplus determined by considering a
value L.sub.c to the succeeding point and left or right turn or
inflection. However, this value b can be set to 0 m. In the case of a
turning corner (inflection), although the succeeding point is decided, it
is also possible to use the area judge value L.sub.c and the area pass
judge value MM to determine that the vehicle has passed the corner point.
If YES (an intersection) in step S.sub.48, the area judge value L.sub.c is
calculated as L.sub.ss +L.sub.s, where L.sub.ss is an integrated standard
area judge value at a turning corner point integrated in step S.sub.49 (in
step S.sub.52). That is, in this step, the area judge value at an
intersection is determined on the basis of a distance between two adjacent
intersections, irrespective of the presence or absence of a turning corner
point between two intersections.
For instance, in the case of the routes as shown in FIG. 13(A), the area
judge value to point P.sub.2 from point P.sub.1 is determined as L.sub.1 x
0.1, and the area judge value to P.sub.6 from point P.sub.3 is determined
as
L.sub.2 .times.0.1+L.sub.3 .times.0.1=L.sub.ss
L.sub.4 .times.0.1=L.sub.s
L.sub.ss +L.sub.s =(L.sub.2 +L.sub.3 +L.sub.4).times.0.1
Further, black dots shown in FIG. 13(A) indicate corrected vehicle
locations.
Thereafter, the integrated standard value L.sub.ss is set to 0 and the area
pass judge value MM is calculated as L.sub.c +b (b: 20 m) (in step
S.sub.53). By doing this, it is possible to determine an area judge value
at an intersection large enough to cover an error produced at a turning
corner point or inflection. Control checks whether the area judge value
L.sub.c is larger than the distance L.sub.n between the current location
and the succeeding point (in step S.sub.54). If YES, 1 m is subtracted
from L.sub.n to obtain a new area judge value L.sub.c (in step S.sub.55).
If NO, control skips step S.sub.55 to step S.sub.56.
Control determines whether the area judge value L.sub.c is smaller than c
(e.g. 10 m) (in step S.sub.56). If YES, the area judge value L.sub.c is
set to c and the area pass judge value MM is set to c+b(10 m+20 m) (in
step S.sub.57), proceeding to the step S.sub.5 shown in FIG. 7. In
summary, steps 56 and 57 can determine the minimum area judge values
L.sub.c and MM. As described above, the route judge area including an area
judge value L.sub.c and an area pass judge value MM has been determined
under considerations of route conditions to an adjacent point and straight
routes within a curved road. Thereafter, control proceeds to step S.sub.5
shown in FIG. 7.
With reference to FIG. 7 again, each data is set (in step S.sub.5) as
follows:
.delta.S.sub.n (sampling distance)=0, .delta..theta..sub.n =0, X.sub.n
=X.sub.00, Y.sub.n =Y.sub.00, .theta..sub.n =.theta..sub.0
Further, the calculated data .theta..sub.0, .theta..sub.2, .theta..sub.3,
L.sub.n, .delta.S.sub.n =0, .delta..theta..sub.n =0, X.sub.n =X.sub.00,
Y.sub.n =Y.sub.00 are all stored in the RAM 15 for sampling calculation of
each vehicle travel distance .delta.S.sub.n and each vehicle travel angle
.delta..theta..sub.n. (in step S.sub.5).
The next sampling calculation (step S.sub.6) can be implemented in
accordance with a subroutine as shown in FIG. 9.
Each travel distance signal S.sub.se from the travel distance sensor 11 and
each travel angle signal .theta..sub.se (.intg.wdt) from the angular rate
sensor 12 are both inputted (in step S.sub.61).
Further, the obtained travel distance S.sub.se and the travel angle
.theta..sub.se are integrated to obtain .delta.S.sub.n =.delta.S.sub.se
and .delta..theta..sub.n =.delta..theta..sub.se (in step S.sub.62), and
then CPU checks whether a predetermined time (e.g. 1 sec) has elapsed (in
step S.sub.63). If YES, the integrated angle value .delta..theta..sub.n is
added to the current angle .theta..sub.n-1 stored in the RAM 15 to obtain
an updated angle value .theta..sub.n. The obtained value .theta..sub.n is
stored in the RAM 15. On the basis of the current angle value
.theta..sub.n, the current corrected location P.sub.n (X.sub.n, Y.sub.n)
can be obtained as follows (in step S.sub.64):
X.sub.n =X.sub.n-1 +.delta.S.sub.n cos .theta..sub.n
Y.sub.n =Y.sub.n-1 +.delta.S.sub.n sin .theta..sub.n
where P.sub.n-1 (X.sub.n-1, Y.sub.n-1) are coordinates stored in the RAM 15
as the preceding location such as P.sub.00 (X.sub.00, Y.sub.00). By the
above correction, it is possible to correctly track the vehicle travel
trace along the road on the map.
In the same way, on the basis of the calculated angle value .theta..sub.1,
the current non-corrected (sensor-detected) location P(x.sub.n, y.sub.n)
can be obtained as follows (in step S.sub.64):
x.sub.n =x.sub.n-1 +.delta.S.sub.n cos .theta..sub.n
y.sub.n =y.sub.n-1 +S.sub.n sin .theta..sub.n
By the above calculation, it is possible to display the current vehicle
location as it is without correction on the map.
In the above-mentioned tracking on the map, the tracking display moves
.delta.S.sub.n by .delta.S.sub.n from a designated point P.sub.00 along a
route R.sub.0 connecting P.sub.00 and P.sub.1 (in step S.sub.64).
Thereafter, the integrated travel distance .delta.S.sub.n and the
integrated travel angle .delta..theta..sub.n are reset when the vehicle
reaches a route judge area (in step S.sub.65).
Control checks whether it is necessary to change the map now displayed on
the basis of the current location coordinates P.sub.n (X.sub.n, Y.sub.n)
and/or (x.sub.n, y.sub.n) (in step S.sub.66). If YES, the map is changed
(in step S.sub.67). If NO, control skips step S.sub.67 to step S.sub.68.
Control checks whether flag is 1 (in step S.sub.68). This flag D
determines coordinates of the current location to be displayed. If YES
(D=1 in step S.sub.68), the current location is displayed by the
non-corrected coordinates (x.sub.1, y.sub.1) based upon the sensors. If NO
(D=0 in step S.sub.68), the current location is displayed by the corrected
coordinates (X.sub.1, Y.sub.1) based upon the coorecting calculation. That
is, the displayed coordinates are determined by this flag D. Thereafter,
control returns to step S.sub.7 shown in FIG. 7.
Returning to FIG. 7, CPU checks whether the number of routes selectable at
the next point P.sub.1 (i.e. the number of branch points) is more than 1
(in step S.sub.7). If NO, flag B is set to 1 (in step S.sub.8) and
proceeds to step S.sub.9. If YES, CPU directly proceeds to step S.sub.9.
Control checks whether the integrated travel distance .delta.S.sub.n is
zero (in step S.sub.9). If YES, since this indicates that the vehicle is
kept stopped, control returns to step S.sub.6. If NO, since this indicates
that the vehicle is moving, control proceeds to the succeeding step. The
current distance L.sub.n between P.sub.00 and P.sub.1 is set as L.sub.n
=L.sub.n-1 -.delta.S.sub.n (in step S.sub.10). That is, in FIG. 6, a
travel distance .delta.S.sub.n is subtracted from the distance L.sub.n
between two points P.sub.00 and P.sub.1 to obtain an updated distance
L.sub.n+1 to the point P.sub.1. Control checks whether the updated
distance L.sub.n becomes less than an area judging valve L.sub.c (e.g. 20
m) indicative of the range of the route judge area JE (in step S.sub.11).
If NO, control returns to the step S.sub.6. If YES, control proceeds to
the succeeding step because this indicates that the vehicle approaches a
branch point. Therefore, the L.sub.m (distance between the current point
to the branch point P.sub.1) is set to zero and the flag D is set to 1 in
order to display the current location on the basis of the non-corrected
location (x.sub.n, y.sub.n) (in step S.sub.12). Control proceeds to the
step S.sub.13 (the same as step S.sub.6 shown in FIG. 9). In this step
S.sub.13, the sampling calculation starts.
In the succeeding step, control sets L.sub.m-1 +.delta.S.sub.n =L.sub.m (in
step S.sub.14). That is, in FIG. 6, a travel distance .delta.S.sub.n is
integrated to obtain a distance away from a point P.sub.a where the
vehicle enters the route judge area JE. Thereafter, control checks whether
L.sub.m exceeds an area pass judge value MM (e.g. 30 m) (in step
S.sub.15). If NO, control returns to the step S.sub.13 to continuously
obtain travel distance .delta.S.sub.n. If YES, since this indicates that a
distance L.sub.m away from a position P.sub.a where the vehicle enters
into the route judge area JE exceeds an area pass judge valve MM (e.g. 30
m) at the branch point P.sub.1, control determines that the vehicle has
passed through the branch point P.sub.1.
After control determines that the vehicle has passed through the point
P.sub.1 in step S.sub.15, control checks whether the angle change
.delta..theta..sub.n is 20 degrees/sec or more or not (in step S.sub.16).
If .delta..theta..sub.n is more than 2 deg/sec, control determines that
the vehicle is not yet turned completely, proceeding to the step S.sub.17.
Control checks the route condition of the succeeding point on the basis of
the flag P (indicative of a special point at the next route set in step
S.sub.43 or S.sub.45 (in step S.sub.17). If P=1, since this indicates that
there exists a special point (e.g. short distance) in the succeeding route
and therefore it is impossible to provide an extension for the area pass
judge value MM, control proceeds to step 18. If P=0, since this indicates
that there exists no specia | | |
