Data processing: vehicles – navigation – and relative location – Navigation – Employing position determining equipment
Reexamination Certificate
2002-04-26
2003-06-03
Cuchlinski, Jr., William A (Department: 3661)
Data processing: vehicles, navigation, and relative location
Navigation
Employing position determining equipment
C701S214000, C342S357490, C342S357490, C342S357490
Reexamination Certificate
active
06574557
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a technical field of a navigation apparatus, and more particularly to a technical field of an apparatus for evaluating positioning data obtained by GPS navigation.
2. Description of the Related Art
In navigation apparatuses, as one of techniques for following up a vehicle or the like by detecting its current position, a positioning method which obtains a position of a vehicle based on a satellite signal (GPS signal) transmitted from a GPS (Global Positioning System) satellite has been generally widespread (which will be referred to as GPS navigation hereinafter).
The accuracy of a position obtained by positioning calculation in the GPS navigation is determined by the satellite arrangement of satellites (basically, not less than four) which transmit GPS signals and the measurement accuracy of a distance from a vehicle, which has received the GPS signals, to each GPS satellite (which will be referred to as a pseudo-range hereinafter).
Further, in recent years, there has been adopted a method which carries out map matching with a map data base by using both the GPS navigation and dead-reckoning which obtains a traveling trajectory by using a gyro sensor and a vehicle speed sensor (which will be simply referred to as dead-reckoning hereinafter).
In such a technique, in case of using a positioning result actually obtained by the GPS navigation in a car navigation apparatus, when a vehicle's own position obtained by the dead-reckoning or map matching largely deviates from a positioning result obtained by the GPS for example, the vehicle's own position is reset to a position of this positioning result, or this result is utilized for selecting a matching position candidate used in map matching.
On the other hand, since the positioning result actually obtained by the GPS navigation includes an error of, e.g., the system or arrangement of the GPS satellites, an error in the positioning result must be taken into consideration in order to use the result positioned by the GPS signal for evaluation of the vehicle's own position.
More specifically, for example, there is a method which uses an error coefficient called a DOP (Dilution of Precision) value determined by arrangement of the GPS satellites and enables the positioning result obtained by the GPS navigation. This method enables the positioning result obtained by the GPS navigation only when the DOP value in the received GPS signal is equal to or below a fixed value.
When a distance to a satellite observed in sole positioning of each GPS satellite includes an error at a fixed level, this DOP value is an index value used for estimating how this error affects the positioning result. As typical DOP values, there are a DOP (HDOP) value in the horizontal direction, a DOP (VDOP) value in the vertical direction and a DOP (PDOP) value in the horizontal/vertical directions.
Furthermore, there is a method which calculates a range in which a vehicle may possibly exist (positioning error range (which will be simply referred to as an error range hereunder)) based on the DOP value and evaluates the inside of this range as a correct position of the vehicle.
In this method, a radius of a circle is obtained by a product of the DOP value and a measurement error in a pseudo-range in each of a plurality of satellites, i.e., (Expression 1), and the vehicle's own position is evaluated with an area in the circle (which will be referred to as an error distribution circle hereinafter) range generated by the radius being determined as a range in which the vehicle may exists.
Error distribution circuit (radius)=
HDOP
×Measurement error of pseudo-range (1)
It is to be noted that a maximum value in the measurement errors of a plurality of obtained pseudo-ranges or a mean value of the measurement errors of the respective pseudo-ranges is used as the measurement error of the pseudo-range used for calculation in this method.
On the other hand, there is a method which obtains the error range determined by the GPS satellite arrangement by calculating a probability error ellipse (which will be referred to as an error ellipse hereinafter) without using the DOP value.
According to the method using the error ellipse, an error ellipse which is an error range is calculated based on the arrangement of the GPS satellites used for positioning and a pseudo-range error in each GPS satellite, and the vehicle's own position is evaluated as an area that the vehicle may exists in any range in the error ellipse.
This error ellipse shows the distribution of the position error which two-dimensionally distributes when components of the position error in a positioning result in the latitudinal direction and the longitudinal direction normally distribute. Specifically, calculation is carried out by using a standard deviation of an error in the latitudinal direction, a standard deviation of an error in the longitudinal direction and the correlation function of the respective standard deviations. Moreover, as represented by Expression (2), in regard to the error ellipse actually used for accuracy evaluation, an ellipse (true error ellipse) is calculated by multiplying the error ellipse calculated as described above by the measurement error of the pseudo-range in the actual GPS satellite.
Error ellipse (true)=Error ellipse (for example, an error is assumed as 1 m)×Measurement Error of Pseudo-range (2)
Incidentally, assuming that measurement errors of distances to all the satellites are constant (for example, 1 m), the shape of ellipse (long axis, short axis, inclination) can be readily calculated.
In addition, the error ellipse presumed to be 1 m is a reference error ellipse generated by assuming that the pseudo-range error in each GPS signal is 1 m. The true range of the error ellipse can be, therefore, represented by multiplying the error ellipse presumed to be 1 m by the measurement error of the pseudo-range in the GPS signal.
It is often the case that a value obtained by adding an accuracy value of the pseudo-range error broadcasted from each satellite (which will be referred to as UERE (User Equivalent Range Error)) and the measurement error caused due to noise generated in the GPS receiver is used as the error value of the pseudo-range of the satellite. The validity of the vehicle's own position can be judged based on the relationship between the ellipse and the vehicle's own position.
In case of the method using the above-described DOP value, however, the error distribution actually outputted by the GPS receiver becomes an ellipse instead of a circle because of the arrangement of the GPS satellites used for positioning, and hence there is a problem that the vehicle's own position can not be correctly evaluated (when the ellipse becomes oblong in particular).
For example, as shown in
FIG. 4
, assuming that the vehicle's own position calculated by the dead-reckoning is a point a and a positioning result positioned based on the GPS signal is a point b, since the point a is included in both the error distribution circle A obtained by the DOP value generated based on the point b of the positioning result and the error ellipse B obtained by the arrangement of the GPS satellites generated based on the point b of the positioning result, an error is not produced in an evaluation result of the vehicle's own position. However, when the vehicle's own position is a point c for example, the point b of the evaluation result differs. That is, although the vehicle's own position is evaluated as inappropriate in the error ellipse representing the further accurate error range, it is determined as appropriate in the error distribution circle.
Additionally, in the method using the error ellipse mentioned above, there is not included the measurement error in the pseudo-range which inherently occurs depending on a position of each GPS receiver such as multi-path. Therefore, in a place where the large multi-path occ
Cuchlinski, Jr. William A
Marc-Coleman Marthe Y.
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