Data processing: vehicles – navigation – and relative location – Navigation – Employing position determining equipment
Reexamination Certificate
2001-11-14
2003-06-17
Black, Thomas G. (Department: 3663)
Data processing: vehicles, navigation, and relative location
Navigation
Employing position determining equipment
C701S207000, C701S200000, C701S117000, C340S990000, C340S995190, C340S988000, C702S094000, C702S150000, C342S357490
Reexamination Certificate
active
06581005
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a vehicle position calculation apparatus and method for accurately determining a vehicle position on a map route in a navigation system for a vehicle.
In such a vehicular navigation system, it has been a usual practice to utilize a vehicle position calculation apparatus which employs a map matching technique for calculating a vehicle position to be displayed on a map route.
The map matching technique strictly operates on an assumption in that the vehicle travels on the road. In particular, measuring sensors include a GPS receiver, a gyro sensor and a vehicle speed sensor which provide a vehicle position and a vehicle travel direction. The vehicle position and the vehicle travel direction are compared with a group of line segments, representing a road shape, which are preliminarily stored in a memory section, thereby correcting the vehicle position so as to lye on a particular point on the line segment having the most probable relationship in a position and a direction in conjunction with the measured value.
Firstly, a vehicle position correction method in the related art is described below in detail with reference to a branch road shown in
FIG. 22
to exemplify how correction of the vehicle position is performed in the branch road.
In
FIG. 22
, it is assumed that the branch road B is given as a correction shape for the vehicle position and is constructed of three line segments L
1
, L
2
, L
3
connected with each other and diverging at a node N. In this respect, it is a usual practice to define a road shape with a plurality of nodes determined at respective positions (with latitude and longitude) and line segments representing a connecting relationship relative to the respective nodes. The road shape thus defined in such a configuration is used for effectuating a map matching operation as will be hereinafter described in detail.
In
FIG. 22
, points P
1
to P
7
refer to measured values or measured points of the vehicle position which is measured with the measuring sensors at time instants t
1
to t
7
. Also, points Q
1
to Q
7
refer to corrected and outputted vehicle positions which are extracted in the vehicle position calculation of the related art. In actual practice, the measured values of the vehicle position are obtained by the measuring sensors to directly provide the coordinate value Pn in an absolute value or to individually provide a vehicle travel direction &thgr;n−1, n and a traveled distance &lgr;n−1, n in a relative value between associated measuring points.
In the former case, the point Pn which is directly measured is hereinafter referred to as a primary vehicle position. In the latter case, also, assuming that a previous measured value is Pn−1, an absolute coordinate value Pn is given by:
Pn=Pn−
1
+&lgr;n−
1,
n exp
(
i&thgr;n−
1,
n
) (1)
wherein exp is an index factor and i is an imaginary unit.
The vehicle position thus obtained is hereinafter referred to as a secondary vehicle position.
The primary and secondary vehicle positions are collectively called as a measured value of the vehicle position. Even in the former case, it is possible to calculate back the relative displacement value &thgr;n−1, n and &lgr;n−1, n from the above equation (1).
Now, at the time instant t
1
, the measured value P
1
of the vehicle position substantially lies on the line segment L
1
and, because a previous vehicle travel direction is substantially aligned with a direction of the line segment L
1
, the measured point P
1
and a corrected result Q
1
are assumed to lye on the same point.
Next, at the time instant t
2
, the measured value of the vehicle position has the point P
2
which is dislocated from the line segment L
1
. If, in this instance, there is no line segment, in close proximity to the measured point, for correcting the vehicle position, except for the line segment L
1
and the vehicle travel direction Q
1
,
2
is oriented at an angle within an allowable error range, then, it is assumed that the vehicle travels on the same road as that the vehicle has previously traveled. That is, it is discriminated that the vehicle position at the time instant t
2
still lies on the line segment L
1
. Accordingly, the vehicle position at this time instant is corrected to a point Q
2
at which a leg of a vertical line drawing from the point P
2
intersects the line segment L
1
.
Further, at the time instant t
3
, it is assumed that the point P
3
is given as the primary vehicle position, or the vehicle travel direction &thgr;
2
,
3
and the traveled distance &lgr;
2
,
3
are obtained between the time interval t
2
, t
3
. At the previous time instant t
2
, the vehicle position is corrected at the point Q
2
on the line segment L
1
. In such a case, assuming that the degree of precision of the relative displacement value is guaranteed to some extent, then, the point P
3
′ is obtained as the secondary vehicle position on the basis of a reference of the previous corrected value as expressed by:
P
3
′=Q
2
+&lgr;
2
,
3
exp
(
i
&thgr;
2
,
3
) (2)
Here, if the point P
3
′ does not lye on the line segment L
1
, then, the measured point of the vehicle position is corrected at the point on the line segment L
1
in the same manner as that achieved in the previous case. For example, the correction is implemented by drawing the leg of the vertical line from the point P
3
′ to the line segment L
1
to output the corrected point Q
3
as a final corrected position. At subsequent steps after the time instant t
3
, similar operations are carried out.
In accordance with the vehicle position calculation method discussed above, as far as a premise satisfies that the vehicle travels on the road, even when the output value of the measuring sensor contains a slight amount of detection error, the detection error is corrected to accurately align the vehicle position with a correct position of the map route in a reliable manner.
Besides, in another related art, it has been proposed that a vehicle position calculation apparatus employs a CD-ROM, which preliminarily stores a plurality of road links with a road being represented with line segments, to enable map matching operation to allow the road links in the vicinity of the vehicle position to be read out from the CD-ROM such that the vehicle position is forced to lye on the road link.
SUMMARY OF THE INVENTION
However, in the first related art discussed above, in a case where the road shape which serves as a ground for correction of the vehicle position is different from an actual road shape, correction of the vehicle position causes a cumulative error, with a resultant output of an erroneous vehicle position.
More particularly, as seen in
FIG. 22
, an actual road shape has an increased road width in front of a branching point and the vehicle, which tends to travels on the line segment L
3
, is supposed to be closer to the left side than the line segment L
1
fairly in front of the node N during traveling. Such a structure is found in the road which has a lane for deceleration of the vehicles at a location in which an exit road diverges from a main road such as an interchange in high-way road.
As a consequence, the measured values P
1
to P
7
shown in
FIG. 22
show a position rather closer to an actual road when the vehicle is going to get out the line segment L
3
. However, in accordance with the former related art, the map matching technique causes the vehicle position to be corrected with respect to the main road. That is, during the time period between t
1
to t
5
, the respective measured points of the vehicle position are corrected at the corrected points Q
1
to Q
5
on the line segment L
1
.
However, at the time instant t
6
shown in
FIG. 23
, even if the measured point P
6
is given under a condition that the accuracy of the relative displacement value is guaranteed, the previous correcting position Q
5
is used as the reference based on which the secondary v
Minakawa Rumi
Nakayama Okihiko
Saitou Hiroshi
Watanabe Masaki
Black Thomas G.
Nissan Motor Co,. Ltd.
To Tuan C
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