Apparatus for generating a heading signal for a land vehicle

Claim 3

The apparatus of claim 1, wherein the subset includes one direction signal from the plurality of independent direction signals.

Claim 4

The apparatus of claim 1, wherein the subset includes all of the direction signals from the plurality of independent direction signals.

Claim 7

The apparatus of claim 4, wherein the subset includes one direction signal from the plurality of independent direction signals.

Claim 8

The apparatus of claim 4, wherein the subset includes all of the direction signals from the plurality of independent direction signals.

Claim 11

The apparatus of claim 7, wherein said filter means includes means, responsive to a filter control signal, for varying said filter characteristics; and means for generating said filter control signal in response to said first direction signal and said second direction signal.

Claim 14

The apparatus of claim 9, wherein: said parameter indicates an estimated magnitude of a combination of the error components of said relative direction signal and said absolute direction signal.

Claim 15

The apparatus of claim 9, wherein said second means comprises: compass means for generating a compass signal indicating the heading of the land vehicle relative to the magnetic field of the earth.

Claim 16

The apparatus of claim 9, wherein said second means comprises: compass means for generating a compass signal indicating the heading of the land vehicle relative to the magnetic field of the earth and including a magnitude component; and further including means for generating said parameter by detecting fluctuations in said magnitude component of said compass signal relative to the expected magnitude of the magnetic field of the earth.

Claim 17

The apparatus of claim 12, wherein said means for generating said parameter includes: means for receiving the magnitude component of the compass signal generated by said compass means; means for storing a table of expected magnitudes of the magnetic field of the earth for a set of directions; means for comparing the magnitude component of the compass signal generated by said compass means with the expected magnitude of the magnetic field of the earth from said table to generate a difference signal; and means responsive to said difference signal to generate said parameter.

Claim 18

The apparatus of claim 10, wherein said second means comprises: compass means for generating a compass signal having a directional component indicating the heading of the land vehicle; and further including means for combining said relative direction signal and the directional component of said compass signal to generate a combined error signal; and means for generating a deviation statistic over a sequence of signal measurements indicating deviation of said combined error signal from an average over said sequence of signal measurements; and means responsive to said deviation statistic for generating said parameter.

Claim 19

The apparatus of claim 9, wherein said first sensor means comprises: differential odometer sensor means for generating said relative direction signal.

Claim 20

The apparatus of claim 9, wherein said first means comprises: differential odometer sensor means for generating said relative direction signal; and further including means for generating said parameter by measuring the velocity and ratio of turn of said vehicle.

Claim 21

The apparatus of claim 9, wherein said second means comprises: compass means for generating compass heading data indicating the heading of the land vehicle relative to the direction of the magnetic field of the earth; means for providing a map data base including entries identifying a street segment and a predicted heading of a land vehicle on the street segment identified in the entry; selector means, responsive to a selection signal, for selecting said compass heading data or a predicted heading in a map data base entry as said absolute direction signal; and selector control means for supplying said selection signal.

Claim 22

The apparatus of claim 17, wherein said selector control means is responsive to a first parameter, and further including: means for generating the first parameter in response to the difference between an estimated heading of the land vehicle and the predicted heading identified in a map data base entry.

Claim 23

The apparatus of claim 17, wherein said selector control means is responsive to a first parameter, and the map data base entries further include an error flag that is set when the compass heading data is expected to be inaccurate for the street segment identified in the entry, and further including: means for supplying the error flag as said first parameter for selection of said predicted heading identified in the map data base entry when the vehicle is located on the street segment.

Claim 24

The apparatus of claim 17, wherein said selector control means is responsive to a first parameter, and further including: means for storing data identifying map data base entries identifying street segments in geographic locations having characteristics which cause said compass means to be inaccurate; and means for supplying said first parameter for selection of said predicted heading identified in the map data base entry when the vehicle is located within one of said geographic locations.

Claim 25

The apparatus of claim 17, further including: a vehicle navigation system for locating the land vehicle; and said selection signal is supplied to said vehicle navigation system as a parameter used in locating the land vehicle.

Claim 26

The apparatus of claim 9, wherein said second means comprises: compass means for generating compass heading data indicating heading of the land vehicle relative to the direction of the magnetic field of the earth; means for providing a map database including entries identifying a street segment and a predicted heading of a land vehicle on the street segment; means, in communication with the compass means and the means for providing a map database and responsive to a control signal for supplying said absolute direction signal based on the compass heading data, and a predicted heading identified in a map database entry; and control means for supplying said control signal.

Claim 27

The apparatus of claim 17, further including: means for supplying to the selector means an entry in the map data base that identifies the street segment on which the land vehicle is located.

Claim 32

In a vehicle navigation system for automatically tracking a motor vehicle movable over a given area identified by a map, an apparatus for generating an estimated heading of the motor vehicle, comprising: first means for generating a relative direction signal including heading information indicating a heading direction of the motor vehicle relative to a prior heading of the motor vehicle and including first errors; second means for generating an absolute direction signal including heading information indicating a heading direction for the motor vehicle relative to the earth and including second errors, said second means including compass means for generating compass heading data indicating the heading of the motor vehicle relative to the earth, means for providing a map data base including entries, each identifying a street segment and a predicted heading of a motor vehicle on the street segment, means, in communication with said compass means and said means providing a map data base and responsive to a control signal, said compass heading data or a predicted heading identified in a map data base entry, for supplying said absolute direction signal, and means, for supplying said control signal; first combining means for subtracting said relative direction signal from said absolute direction signal to generate a combined error signal; filter means, responsive to a filter control signal, for filtering said combined error signal to essentially cancel said second errors and generate a filtered error signal, said filter means including means for generating said filter control signal in response to at least one parameter indicating the estimated magnitude of at least one of said first and second errors; and second combining means for adding said filtered error signal to said relative direction signal to essentially cancel said first errors in said relative direction signal to generate the estimated heading of the motor vehicle.

Claim 33

In a vehicle navigation system for automatically tracking a motor vehicle movable over a given area identified by a map, an apparatus for generating an estimated heading of the motor vehicle, comprising: first means for generating a relative direction signal including heading information indicating a heading direction of the motor vehicle relative to a prior heading of the motor vehicle and including first errors; second means for generating an absolute direction signal including heading information indicating a heading direction for the motor vehicle relative to the earth and including second errors, said second means including compass means for generating compass heading data indicating the heading of the motor vehicle relative to the earth, means for providing a map data base including entries, each identifying a street segment and a predicted heading of a motor vehicle on the street segment, means, in communication with said compass means and said means providing a map data base and responsive to a control signal, said compass heading data or a predicted heading identified in a map data base entry, for supplying said absolute direction signal, and means, for supplying said control signal; first combining means for subtracting said relative direction signal from said absolute direction signal to generate a combined error signal; filter means, responsive to a filter control signal, for filtering said combined error signal to essentially cancel said second errors and generate a filtered error signal, said filter means including means for generating said filter control signal in response to at least one parameter indicating the estimated magnitude of at least one of said first and second errors; and second combining means for adding said filtered error signal to said relative direction signal to essentially cancel said first errors in said relative direction signal to generate the estimated heading of the motor vehicle.

Claim 36

The apparatus of claim 27, wherein said means for generating said parameter is further responsive to the estimated magnitude of the error components of both the absolute direction signal and the relative direction signal.