Apparatus for displaying current location

There is disclosed an apparatus for displaying a current location of a running body in which a constantly changing location of the running body on a two-dimensional coordinates is successively computed, while detecting a running distance of the running body and a running direction of the same, and the current location of said running body is displayed renewally, in accordance with the data thus computed, on a display screen having a map previously displayed thereon. The apparatus comprises means for extracting a linear running portion from current location of the running body obtained by storing data of the current location, means for extracting a linear road portion from adjoining roads on the map which corresponds to the linear running portion extracted from the current location means for effecting matching between the extracted linear running portion and linear road portion, depending on their positional relationship and means for putting the current location, onto the road to which the matching has been effected.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a current location displaying apparatus in 
which a path of travel of a running body, such as an automobile, is 
displayed on a display screen which has a map perviously displayed 
thereon. 
2. Description of the Prior Art 
Recently, in an attempt to provide guidance to a driver of an automobile to 
prevent the driver from losing his way, during driving, for example, in a 
strange place, there has been developed a current location displaying 
apparatus, as hereinafter described more in detail, in which a running 
distance and a running direction of the running body are detected, from 
time to time, and a current location of the running body on 
two-dimensional coordinates is successively computed from results of such 
detections, whereby the current location of the running body is 
successively displayed on a map which is previously displayed on a screen. 
In such current location displaying apparatus, it is difficult to avoid 
occurrence of a positional error owing to precision of detections at the 
time of detecting the distance and the direction during running of the 
running body, and such positional error is progressively integrated, as 
the running body continues its running, with the result that the current 
location comes off the running course on the map until the driver becomes 
unable to see where he is driving. 
One pratice to correct such positional error by effecting matching between 
a pattern of a road on a map and a pattern of current location of the 
running body which is obtained by storing and holding data of the 
successively changing current location as the running body continues its 
running, thereby enabling correction of the current location which has 
come off the running course. According to this method, a plurality of 
roads which are considered to be the roads through which the running body 
has passed are selected from a complicated road network in any manner, and 
adaptability of the pattern of each of the extracted roads and the pattern 
of the current location of the moving body is examined. Then, the road 
having highest matching rate is assumed as a road where the running body 
is actually running and the correction in position is effected as the 
current location of the moving body comes onto the road to which the 
matching has been effected. 
In such method, if the map includes complicated roads, considerable number 
of road patterns are extracted as the roads which are considered to be the 
ones through which the moving body has passed. 
It is, therefore, necessary to effect matching of the pattern of the travel 
path to each of the road patterns, so that the processing is very 
complicated and requires considerable time. This method has a further 
disadvantage in that if the running body passes through a road which does 
not exist on the map, the pattern matching cannot be effected, with the 
result that the correction of the current location becomes impossible. 
OBJECT OF THE INVENTION 
In view of the disadvantages of these other systems it is an object of the 
present invention to provide a current location displaying apparatus in 
which a current location of a running body which has come off a running 
course is corrected by effecting matching of a pattern of a road on a map 
and a pattern of a travel path of the running body, which enables the 
apparatus to continue processing, even if the running body temporarily 
passes through a road which does not exist on the map, and to effectively 
and precisely effect matching between a road pattern and a travel path 
pattern. 
SUMMARY OF THE INVENTION 
In order to attain the object as described above, the present invention 
provides an apparatus for displaying a current location of a running body 
in which a constantly changing location of the running body on 
two-dimensional coordinates is renewably computed, while detecting a 
running distance of the running body and a running direction of the same, 
and the current location of said running body is displayed renewably, in 
accordance with the data thus computed, on a display screen having a map 
previously displayed thereon, which comprises means for extracting a 
linear running portion from the travel path of the running body obtained 
by storing data of the current location, means for extracting a linear 
road portion from adjoining roads on the map which corresponds to the 
linear running portion extracted from the travel path, means for effecting 
matching between the extracted linear running portion and linear road 
portion, depending on their positional relationship and means for putting 
the travel path onto the road to which the matching has been effected.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Now, the description will be made on an embodiment of the present 
invention, with reference to the accompanying drawings. 
FIG. 1 shows an example of the fundamental construction of the current 
location displaying apparatus according to the present invention. The 
essential constituent factors include a distance sensor 1 of 
photoelectric, electromagnetic, mechanical contact type or the like, for 
generating pulse signals corresponding to a travel distance of the running 
body, depending upon the rotation of the wheel of said running body, for 
example; a direction sensor 2 for generating signals proportional to an 
amount of change of direction of the running body consisting of a 
gyroscope for detecting change of angular velocity of yawing direction, 
for example; a signal processing unit 3 which serves to count the number 
of the pulse signals sent from the distance sensor 1 to measure the 
distance of travel of the running body and also serves to decide the 
change of the running direction of the running body on the basis of the 
output signal of said direction sensor 2 to successively compute the 
current location of the running body on the two-dimensional coordinates at 
every unit distance of travel of the running body to effect centralized 
control of the whole system, said unit 3 including a CPU, a programming 
ROM, a controlling ROM, etc.; a travel path storing means 4 for 
successively storing the data of the constantly changing location on the 
two-dimensional coordinates obtained by said signal processing unit and 
holding said data as finite and continuous location informations 
corresponding to the current locations of the running body; a map 
information storage medium 5 in which a plurality of file units of map 
information is previously stored; a storage medium reader unit 6 for 
selectively reading out the desired map file from the storage medium 5; a 
display unit 7 for displaying a map on a display screen in accordance with 
the read-out map information and renewably displaying the current 
locations of the running body, the path travel and the current running 
direction and the other information on the same display screen on the 
basis of the location data stored in the storage unit 4, and a manual 
operating unit 8 for giving a command for operation to the signal 
processing unit 3 and for effecting various operations including selection 
of the map to be displayed on the display unit 7, setting of the starting 
point of the vehicle on the displayed map, change of directions of the 
displayed map and the travel path, shifting of the displayed position, 
change of the setting of the displayed form such as the partial 
enlargement of the display of the map and the travel path, selection of 
the reduction scale and the like. 
In the construction as described above, the map, which has been selectively 
read out, is displayed on the display unit 7, as shown in FIG. 2, and a 
display mark MI indicating the current location of the running body on the 
X-Y map, depending upon a predetermined map reduction rate previously set 
by the signal processing unit 3 in accordance with the travel of the 
running body from a starting point set on the map, a display mark M2 
indicating the running direction at said current locations and a display 
mark M3 indicating the travel path from the starting point S to the 
current location are simulatively displayed thereon, depending upon the 
running status of the running body. 
The above-described construction and its operation are the same as those of 
the known travel path display apparatus as hereinbefore described. 
Accordingly, this travel path displaying apparatus has such disadvantage 
that the current location and the travel path increasingly come off the 
road on the map as the running body proceeds, owing to the integrated 
error as described above, as shown in FIG. 3, until the driver becomes 
unable to see where he is driving on the map. 
In order to avoid such disadvantage, the current location displaying 
apparatus according to the present invention comprises means for 
extracting a linear running portion from the travel path of the moving 
body, means for extracting a linear road portion from adjoining roads on a 
map which corresponds to the extracted linear runnning portion, means for 
effecting matching between the extracted linear running portion and the 
extracted linear road portion in accordance with the positional 
relationship thereof and means for bringing the current location into line 
with the road to which the matching has been effected. 
Practically, these means are executed in the signal processing unit 3. 
The means for extracting a linear running portion from the travel path of 
the running body is executed in the following manner. The processing 
thereof is shown by a flow chart of FIG. 4. 
Firstly, an initial position A and a running direction .theta..sub.o at 
said position of the moving body, as shown in FIG. 5, are memorized and 
then a running direction .theta., at the time when the moving body has 
moved for a preset distance L1 is decided. A variation .DELTA..theta. of 
the running direction at this stage is calculated 
(.DELTA..theta.=.vertline..theta..vertline.-.theta..sub.o 1). 
Nextly, the variation .DELTA..theta. of the running direction and a preset 
threshold value .theta.th are compared with each other. If 
.DELTA..theta.&lt;.theta.th, it is decided that the running direction at this 
time is stable and the moving body is moving along a straight line of 
.DELTA..theta..gtoreq..theta.th, it is decided that the moving body is not 
moving along a straight line. 
If it is decided that the moving body is moving along a straight line, a 
supposed straight line A--A' is drawn from the initial position A in the 
direction .theta..sub.o and a distance d between the current location P of 
the moving body and the supposed straight line A--A' is found. 
The found distance d and the preset threshold value D are compared with 
each other. As long as the relation d&lt;D is met, it is decided that the 
moving body is continuously moving on the straight line. The value of D is 
set in such degree that it is not effected by a change of traffic lane. 
When the relation becomes d.gtoreq.D, it is supposed that the moving of the 
moving body on the straight line terminates. Then, the running distance on 
the straight line Lx between the current location P of the moving body and 
the initial position A is found and the found running distance on straight 
line Lx and the preset threshold value Lth are compared with each other. 
If Lx&gt;Lth, it is assumed that the linear running portion having a length 
longer than a predetermined length has been detected and the respective 
positions on the coordinates of a beginning point and an ending point of 
said linear running portion are memorized. 
If Lx.ltoreq.Lth, it is assumed that the linear running distance of the 
moving body is short and this linear running portion is excluded, as that 
it is not subjected to the matching process. 
The same steps are repeated and the linear running portions are 
successively detected as the travel path proceeds. 
In this case, the linear running portion having a distance shorter than a 
predetermined value is not subjected to the matching process. However, it 
is possible to set the threshold value Lth stepwise, so that the threshold 
value can be set at a lower value in case where the moving body is running 
on a curved mountain road, for example, so that the shorter linear running 
portion may be subjected to the matching process. 
The means for extracting the linear road portion from the adjoining roads 
on the map which corresponds to the linear running portion extracted from 
the travel path is excuted in the following manner. 
When a linear running portion a-b is detected from the travel path of the 
moving body, as shown in FIG. 6, a road searching area W having a width of 
2R is defined by parallel lines on both sides of the linear running 
portion a-b. Within this area W, a linear road portion having a 
predetermined minimum road length L min and defined by lines having 
difference in angle relative to the linear running portion a-b within a 
threshold value .alpha. is extracted. 
Now, it is assumed that the travel path of the runnnig body relative to the 
road in the map is as shown by a broken line in FIG. 7. 
According to the present invention, firstly linear running lines 11, 12, 13 
and 14 are extracted from the travel path, as shown in FIG. 8(a). 
The portion between the points b and c, in FIG. 8(a), indicates that the 
moving body moves on a road which is not shown in the map. the portions 
d-e and f-g indicates that the moving body curves at intersections. 
Then, proposed linear road portions m1.1 and m1.2 which correspond to the 
extracted linear running portion 11, proposed linear road portions m2.1 
and m2.2 which correspond to the extracted linear running portion 12, a 
proposed linear road portion m3.0 which corresponds to the extracted 
linear running portion 13 and a proposed linear road portion m4.0 which 
corresponds to the extracted linear running portion 14 are extracted 
respectively, as shown in FIG. 8(b). 
Then, a matching rate between each of the extracted travel path portions 
and each of the extracted road portions is found from the positional 
relation therebetween. The found matching rate is compared with a 
predetermined threshold value. The linear road portion having the matching 
rate larger than the threshold value is decided as an optimum one of the 
proposed linear road portion, and the linear running portion in the travel 
path which corresponds to the optimum one of the proposed linear road 
portions is brought into line with the linear running portion. 
If a plurality of linear road portions having the matching rate higher than 
the threshold value are found, the optimum one of the proposed road 
portions is not decided at this time, and the decision is effected 
depending upon the matching process of the succeeding linear portions, 
according to a so-called indecisive algorithm. 
A coordinate transformation may be effected to indicate a straight line on 
X-Y coordinate by points on .theta.-.nu. coordinate, according to Hough 
Transformation, for example, the respective points corresponding to the 
linear portions extracted from the travel path and the road on the map are 
subjected to the matching process, and the positions of the points on the 
.theta.-.gamma. coordinate are adopted as characteristic amounts, to which 
the matching process is effected. In these coordinates, .theta. is an 
angle of a perpendicular drawn from a straight line on the X-Y coordinates 
to an origin of the coordinates and .gamma. is a length of the 
perpendicular. For example, a straight line L on the X-Y coordinates shown 
in FIG. 9 is expressed by a point .theta.1 on the .theta.-.gamma. 
coordinates, as shown in FIG. 10. 
In this case, therefore, the matching process can be easily effected by 
simply comparing the positions of the respective points corresponding to 
the linear portions extracted from the travel path and the road on the 
map. 
It is, of course, possible to directly subject the linear portions 
extracted from the travel path and the road on the map to the matching 
process, so that the matching is effected on the basis of the 
characteristic amounts including the positions on the X-Y coordinates, the 
length, the inclining direction, the inclining angle, etc., but in such 
case many characteristic amounts to be subjected to the matching process 
are included and, therefore, the matching process is troublesome. 
The above matching process is collectively effected every time a 
predetermined number of the linear running portions extracted from the 
travel path has been obtained as the travelling body proceeds. 
Now, it is assumed that the matching process is collectively effected every 
time when four linear running portions have been extracted from the travel 
path, for example. In this case, the relation is as shown in FIG. 8 and 
the combination of the selected four linear running portions 11-14 is as 
shown in FIG. 11. 
This case includes combination of (2.sup.4 -1) from the case where all of 
11-14 are selected to the case where only one of 11-14 is selected. 
For example, it is assumed that the moving body is running in such state 
that the linear running portion 13 of the travel path is on a road which 
is in parallel with a proposed linear road portion and is not shown on the 
map. Then the linear running portion 13 is not selected and the 
combination includes the linear running portions 11, 12 and 14. 
Such combination of the proposed linear road portions on the map is 
effected, depending upon the selected combination of the linear running 
portions of the travel path. 
For example, the combinations of the proposed linear road portions on the 
map corresponding to the combination of selection of the linear running 
portions 11, 12 and 14 of the travel path include four sets .circle.1 - 
.circle.4 as shown in FIG. 12. 
The matching process is executed on every combination including the 
combinations of selection of the linear running portions 11-14 and the 
combinations of the proposed linear road portions on the map. 
Good precision of matching is obtained by executing the matching process on 
all of the combinations. However, it is not always necessary to execute 
the matching process on all combinations, and the matching process may be 
executed on properly selected combinations. 
Further, it is not always necessary to collectively effect the matching 
process. It is, of course, possible to successively execute the matching 
process as the linear running portions are extracted from the travel path. 
When the travel path is brought into line with the road to which the 
matching has been effected, it is possible to individually and 
successively bring the linear running portion extracted from the travel 
path into the optimum one of the linear road portions to which the 
matching has been effected. In case where the matching process is 
collectively effected, it is possible to calculate an average of vectors 
including differences in direction between the corresponding linear 
running portions and linear road portions and sizes of these portions, and 
to displace a group of the linear running portions by a predetermined 
distance in a predetermined direction, depending upon the calculated 
average of the vectors. 
Thus, it will be understood that the present invention provides an 
apparatus in which the matching between the travel path of the moving body 
and the road on the map can be easily and precisely effected, with small 
amount of information, by partial matching process of the linear portions, 
so that the load applied to the signal processing unit 3 is decreased and 
the matching process can be effected at high speed. 
When a coordinate transformation, for example, a Hough Transformation, is 
applied to transform the linear portions extracted from the travel path 
and the road on the map into the points, it is possible to effect the 
matching process by simply comparing the positions of the points on the 
map, that is more advantageous. 
Furthermore, in the apparatus of the present invention, the matching 
between the travel path and the road on the map is affected on the basis 
of the discontinuous linear running portions extracted from the travel 
path, without requiring a process for searching related road portions as 
in the conventional apparatus, so that even if the moving body runs on a 
road which is not shown on the map, the matching process can be effected, 
without being effected thereby. 
According to the present invention the collective process is effected on 
the combination in which the linear running portion extracted from the 
travel path is assumed to be located outside of the road shown on the map 
and, accordingly, the running portion outside of the road on the map is 
automatically cancelled at the time of effecting the matching process, so 
precision of matching is improved. 
Further according to the present invention, a deformation of the map at a 
curved portion does not affect the matching process of the present 
invention, and with regard to a deformation of the map at a straight 
portion the matching rate is rather improved by cancelling the 
deformation. Thus, a toughness against deformations of the map is 
increased. 
For example, a map of a town in which a detailed road map is shown and 
another map of a suburb in which only main roads are shown have no 
corresponding relation with each other. In such case, the present 
invention is effectively applied, since it does not depend upon the 
interrelation between one map and another. 
Thus, the present invention provides a current location displaying 
apparatus in which a linear running portion is extracted from a travel 
path of a moving body, while a linear road portion corresponding thereto 
is extracted from a road on a map; matching process is effected between 
the extracted linear running portion and linear road portion, depending 
upon a positional relationship therebetween, and the current location is 
brought into line with the road to which the matching has been effected. 
Accordingly, the processing is not interrupted even if the moving body 
tentatively comes off a road on a map and the matching process is effected 
always in optimum manner, so that the travel path of the moving body on 
the map is displayed with high precision.