Patent Number: 
Section: claims

1. A navigation system comprising:a global-positioning-system receiver for receiving radio waves transmitted from multiple global-positioning-system satellites and producing a measured position;an error-range setting section for setting an estimated error range in which a measured position at the time of current positioning by the global-positioning-system receiver is included; anda position correcting section for correcting the measured position by using an actual measured position, when the actual measured position produced by the global-positioning-system receiver at the current positioning time is in the estimated error range, and for correcting the measured position in accordance with a relative positional relationship between the actual measured position and the estimated error range, when the actual measured position is out of the estimated error range. 2. The navigation system according to claim 1, wherein the position correcting section corrects the measured position so that the corrected measured position is in the estimated error range. 3. The navigation system according to claim 1, wherein the position correcting section corrects the measured position so that the corrected measured position is located in the estimated error range and is shifted toward the actual measured position. 4. The navigation system according to claim 1, wherein the position correcting section corrects the measured position so that the corrected measured position is located on an outer edge of the estimated error range. 5. The navigation system according to claim 1, wherein the position correcting section corrects the measured position so that the corrected measured position is located on an outer edge of the estimated error range and is shifted toward the actual measured position. 6. The navigation system according to claim 1, wherein the global-positioning-system receiver produces, together with the measured position, a velocity and a travel angle at which the measured position moves, and the error-range-setting section sets the estimated error range in accordance with the velocity and the travel angle. 7. The navigation system according to claim 6, wherein, for the estimated error range, a circumferential width centering at a previous measured position is set with respect to a previous travel angle supplied from the global-positioning-system receiver, considering a travel-angle variable range set based on a previous velocity. 8. The navigation system according to claim 6, wherein, for the estimated error range, a radial width centering at a previous measured position is set with respect to a previous velocity supplied from the global-positioning-system receiver, considering a velocity variable range set based on a previous velocity. 9. The navigation system according to claim 7, wherein the travel-angle variable range is set based on a result obtained by determining, using an actual vehicle, a relationship between velocities produced by the global-positioning-system receiver and a travel-angle fluctuation range. 10. The navigation system according to claim 8, wherein the velocity variable range is set based on a result obtained by determining, using an actual vehicle, a relationship between velocities produced by the global-positioning-system receiver and a velocity fluctuation range. 11. The navigation system according to claim 9, wherein the size of the estimated error range is set to be variable in accordance with a positioning environment. 12. The navigation system according to claim 11, wherein the estimated error range is set to be large, when the positioning environment is favorable. 13. A navigation system comprising:a global-positioning-system receiver for receiving radio waves transmitted from multiple global-positioning-system satellites and producing a measured position and travel angle at which the measured position moves;an error-range setting section for setting an estimated error range in which a measured position at the time of current positioning by the global-positioning-system receiver is included and wherein the estimated error range is set using the travel angle; anda position correcting section for correcting the measured position by using an actual measured position, when the actual measured position produced by the global-positioning-system receiver at the current positioning time is in the estimated error range, and for correcting the measured position in accordance with a relative positional relationship between the actual measured position and the estimated error range, when the actual measured position is out of the estimated error range. 14. The navigation system according to claim 13, wherein the error-range setting section further comprises an estimated-error-range correcting section for correcting the orientation of the estimated error range set by the error-range-setting section, in accordance with the previous value of the travel angle at which the measured position moves and at least one value before the previous value. 15. The navigation system according to claim 14, wherein, in accordance with the previous value of the travel angle at which the measured position moves and the value before the previous value, the estimated-error-range correcting section calculates a direction in which the measured position moves from the previous positioning time to the current positioning time, and corrects the orientation of the estimated error range so that the calculated direction becomes the center of the estimated error range. 16. The navigation system according to claim 14, wherein the estimated-error-range correcting section corrects the orientation of the estimated error range, considering an amount of change in the travel angle. 17. The navigation system according to claim 14, wherein the estimated-error-range correcting section corrects the orientation of the estimated error range, only when a change in the travel angle at which the measured position moves is larger than a reference value. 18. A method of correcting a measured position in a navigation system comprising:receiving radio waves transmitted from multiple global-positioning-system satellites and producing a measured position;setting an estimated error range in which a measured position at the time of current positioning is included; andcorrecting the measured position by using an actual measured position, when the actual measured position at the current positioning time is in the estimated error range, and for correcting the measured position in accordance with a relative positional relationship between the actual measured position and the estimated error range, when the actual measured position is out of the estimated error range. 19. The method according to claim 18, wherein the measured position is corrected so that the corrected measured position is located in the estimated error range and is shifted toward the actual measured position. 20. The method according to claim 18, wherein, together with the measured position, a travel angle at which the measured position moves is produced, and the estimated error range is set in accordance with the travel angle.