| 摘要 |
PROBLEM TO BE SOLVED: To transmit map data to a vehicle at an accurate timing even when a data transmission rate is low by a method wherein the map data at the front in the advance direction of the vehicle is acquired in advance and retained by an on-vehicle apparatus. SOLUTION: A radio telephone 2f is connected to a control part 3b at an on-vehicle apparatus 2 through a modem 2e, and map data is exchanged between the on-vehicle apparatus and a center apparatus 1. The control part 3b transits data on the present position of a vehicle and on its advance direction to the center apparatus 1 and requests map data. The center apparatus 1 retrieves map data on an estimated position at the front in the advance direction of the vehicle and transmits the retrieved map data to the vehicle. In the on-vehicle apparatus 2, the transmitted map data is stored temporarily in a memory 3c for prefetch, and it is then displayed on a display when the vehicle is going out of position on a map which is displayed at present. In this manner, the map data, on the advance direction, which is acquired in advance so as to be stored can be displayed immediately when the vehicle enters its region. |
