Navigation system and a method of calculating GPS measuring deviation

Claim 1

A navigation system comprising: GPS receiving means for receiving satellite information including accuracy information supplied from a plurality of GPS satellites and outputting at least said accuracy information, a measuring position calculated from the satellite information, and a declining rate of measuring accuracy calculated on the basis of the positions of the GPS satellites; deviation calculating means for calculating a GPS measuring deviation by using the accuracy information and the declining rate of measuring accuracy; map information storing means for storing map information including digitized road information; and current position estimating means for estimating a current position by searching the road information within the radius of the GPS measuring deviation around the measured position.

Claim 7

A method of determining a current position of a self-movable body by map-matching in reliance on GPS satellite accuracy information and a declining rate of measuring accuracy supplied from a plurality of GPS satellites, the method comprising steps of: detecting whether GPS satellite information is obtained; obtaining said accuracy information of each captured satellites; obtaining said declining rate of measuring accuracy; detecting whether a measuring dimension is two or three; obtaining URA values from three satellites and obtaining a maximum URA value of the three satellites and using the maximum URA value as a URA of a fourth satellite, if the two measuring dimension is detected; calculating the GPS measuring deviation from said declining rate of measuring accuracy, said URA values of said three satellites and said maximum URA value; and storing the calculated GPS measuring deviation; performing map-matching by searching only road information within a radius around a current measuring position, said radius being equal to said stored GPS measuring deviation, thereby reducing a searching area in said map-matching step when said GPS measuring deviation is low and increasing said searching area when said GPS measuring deviation is high; determining an updated current measuring position from within said radius.

Claim 8

A method of determining a current position of a self-movable body by map-matching in reliance on GPS satellite accuracy information and a declining rate of measuring accuracy supplied from a plurality of GPS satellites, the method comprising steps of: detecting whether GPS satellite information is obtained; obtaining said accuracy information of each captured satellites; obtaining said declining rate of measuring accuracy; detecting whether a measuring dimension is two or three; obtaining URA values from three satellites and obtaining a maximum URA value of the three satellites and using the maximum URA value as a URA of a fourth satellite, if the two measuring dimension is detected; calculating the GPS measuring deviation from said declining rate of measuring accuracy, said URA values of said three satellites and said maximum URA value; and storing the calculated GPS measuring deviation; performing map-matching by searching only road information within a radius around a current measuring position, said radius being equal to said stored GPS measuring deviation, thereby reducing a searching area in said map-matching step when said GPS measuring deviation is low and increasing said searching area when said GPS measuring deviation is high; determining an updated current measuring position from within said radius.