GPS based time determining system and method

In a GPS navigation and audio entertainment system having navigation control means, display means, a GPS receiver for receiving GPS radio wave signals and processing means for determining a current position, the improvement comprising:

• means for determining a reference time of day of said received GPS radio wave signals;
• a data base containing time-related information including time zone position boundaries mapped as a function of geographical position coordinates, said time-related information further including rules for defining changes in time;
• a clock for providing a measured time of day;
• means for determining a direction of travel;
• means for determining a speed of travel;
• means for calculating an approximate current position as a function of the determined direction and speed of travel when GPS radio wave signals are unavailable and calculating the current time of day for the approximate current position;
• and
• means for periodically updating the clock with the calculated current time of day.

A navigation system for use in a vehicle and having a clock which is automatically updated with a measured time of day based on time change boundaries, the system comprising:

• a radio wave receiver for receiving a position indicative signal and a reference time;
• means for determining a current position of the vehicle from the radio wave signal;
• memory containing time-related information including time zone position boundaries mapped as a function of geographical position coordinates, said time-related information further including rules for defining changes in time as a function of the geographical position coordinates;
• a clock for providing a measured time of day;
• means for determining a direction of travel;
• means for determining a speed of travel;
• means for calculating an approximate current position as a function of the determined direction and speed of travel when GPS radio wave signals are unavailable and calculating the current time of day for the approximate current position;
• and
• means for periodically updating the clock with the calculated current updated time of day.