Data processing: vehicles – navigation – and relative location – Navigation – Employing position determining equipment
Reexamination Certificate
1999-09-30
2001-02-13
Cuchlinski, Jr., William A. (Department: 3661)
Data processing: vehicles, navigation, and relative location
Navigation
Employing position determining equipment
C342S357490
Reexamination Certificate
active
06188959
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The invention concerns a navigation device and a method for position determination by means of dead reckoning, in particular for motor vehicles, in which measured values for distances traveled and directions are summed. A position calculated in this way is compared with a probable position on a digitized road map and corrected. The process is called map matching.
German published patent application DE 35 19 277 A1 discloses a navigation method for vehicles which is based on dead reckoning. On reaching a final destination the user can determine the difference between the calculated position and the actual location by pressing a button. This is used to determine correction values for the measurement of the direction and for the measurement of the distance traveled. These correction values can be used to correct inherent, constant errors in the measurement of direction and distance.
International patent application WO 93/09509 discloses a sensor system for vehicle navigation in which an error component of a sensor is determined in order to recalibrate the sensor.
U.S. Pat. No. 5,394,333 describes a hybrid vehicle navigation system with GPS and dead reckoning. A position calculated using dead reckoning is drawn on a road map. The difference between the position on the road map and a position found using GPS is used to determine a correction value for the GPS navigation system.
From German published patent application DE 42 11 933 A1 there is known a navigation device for dead reckoning which produces correction values for a GPS receiver. A correction value is derived by comparing a position calculated by dead reckoning with a road position coordinate read from a mass memory device. This correction value is fed to the GPS receiver in order to adjust the position data acquired via satellite reception. Digitalization errors in the roads stored in mass memory are integrated unfiltered in the correction value.
From German published patent application DE 35 19 277 there is known a navigation method for vehicles with a dead reckoning device in which on reaching a destination a correction value is derived through determination of the difference between the destination entered and the location calculated by dead reckoning.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a navigation device and a method for position determination by means of dead reckoning, which overcomes the above-mentioned disadvantages of the heretofore-known devices and methods of this general type and which allow exact position determination using dead reckoning even if a variable error occurs between the calculated positions and the probable positions.
With the foregoing and other objects in view there is provided, in accordance with the invention, a navigation device for dead reckoning, comprising:
an input for receiving a distance signal from a sensor for determining a distance;
an input for receiving a direction signal from a sensor for determining a direction;
a processor for position calculation based on the distance signal and the direction signal received from the sensors;
a memory device connected to the processor and having stored therein a digitized road map for comparison with a calculated position;
a memory connected to the processor for storing a sequence of deviations between each of a series of calculated positions and a corresponding position on the digitized road map;
the processor being programmed to correct a calculated position using a correction value derived on a basis of saved deviations; and
to save a sequence of deviations for deriving a correction value in the memory until a new deviation to be saved lies outside a defined limit.
In other words, the error between a position calculated by dead reckoning (sensor position) and a probable position on a road map corresponding with this, is saved in memory. From a sequence of errors or deviations, a specific error pattern is derived and used for correcting the position calculated by dead reckoning. The error pattern is not used for making a correction at the level of a direction sensor or distance sensor in order to provide a correction value for the measured angle or distance respectively. According to the invention, a correction takes place at the processor level and not at the sensor level.
In doing this, the corresponding digitized road map position used for deriving the correction value does not have to be a position already evaluated as certain through map matching. It is also possible simply to use the (tracking) position followed on the digitized road map, for which position the degree of certainty that it is the actual position is not high enough for it to be used for dead reckoning navigation.
During the simultaneous tracking on the digitized road map of several paths on which the actual position of the navigation device or a vehicle equipped therewith could be located, several (possible) positions on the digitized road map can correspond with the position calculated by dead reckoning. Of all the possible positions, the one most suitable for determining the difference from the position calculated by dead reckoning is that position on the particular path for which there is the greatest degree of certainty that the actual location lies on it. Some examples of criteria which can be used for determining the degree of certainty are agreement with a path definitely used previously, the level of agreement between a direction measured by a sensor and the direction of the digitized path, and the nearness to the measured position. Alternatively, it is possible to determine and save several differences of a measured (sensor) position from the respective possible corresponding positions on different paths.
As a result of the continuous feedback to the calculated position of the difference between calculated and probable position, a reliable determination of position takes place even if the error pattern changes. This is the case, for example, for direction measurement using a gyroscope with an error dependent on the operating temperature.
In accordance with an added feature of the invention, a new sequence of deviations for derivation of a correction value is saved if the deviations in a sequence do not differ among each other by more the standard deviation of a current sequence or by more than a predefined amount.
In accordance with another feature of the invention, a deviation derived as a difference between the calculated position and the corresponding position on the digitized road map is saved, divided by a number of at least one of distances and directions added since deriving a previous difference.
With the above and other objects in view there is also provided, in accordance with the invention, a method of determining a position by dead reckoning, which comprises the following steps:
acquiring measured values for a distance traveled and a direction;
forming vectors from the measured values for the distance traveled and for the direction and summing the vectors with a processor;
determining a difference between a calculated position and a corresponding probable position on a digitized road map and saving the difference as a deviation from the probable position;
calculating a correction value based on chronologically sequential deviations; and
adding each correction value to a subsequently calculated position.
In accordance with again an added feature of the invention, the correction value is derived on a basis of the mean of the deviations.
According to a preferred embodiment, a rapid change in the error pattern is not reflected in the correction value. This can be achieved, for example, by defining a limit for the divergence of a new difference from the differences already saved. In this way a recognized difference which is based on an error in the digitalization of the road map is not integrated into the correction value. A similar error can also occur depending on the lane chosen when negotiating curves on wide roads, or in the case that a passenger vehicl
Cuchlinski Jr. William A.
Gibson Eric M
Greenberg Laurence A.
Lerner Herbert L.
Siemens Aktiengesellschaft
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