THREE-DIMENSIONAL MAP DISPLAY SYSTEM

摘要

A map database stores three-dimensional polygons of features, as well as water system polygons such as sea and lake and ground surface polygons. The map database stores map data in multiple levels having different levels of details, such as levels LVa to LVc. A procedure of displaying a three-dimensional map offsets the water systems relative to the ground surfaces, draws a map of a distant view area distant away from the viewpoint using map data at a low level of details, subsequently clears a depth buffer and newly draws a map of a close view area close to the viewpoint using map data at a high level of details. The offset is set to increase in the distant view area and decrease in the close view area. Increasing the offset in the distant view area avoids the occurrence of Z-fighting in the distant area from the viewpoint.

主权项

1. A three-dimensional map display system that displays a three-dimensional map, comprising:
a map database that stores three-dimensional polygon data representing geography and a three-dimensional shape of each feature; an offset setting section that performs an offset process in an overlapping area of a first polygon and a second polygon representing substantially horizontal planes to shift the first polygon and the second polygon relative to each other in a height direction, so as to make a height difference between the first polygon and the second polygon; and a drawing controller that uses the three-dimensional polygon data and polygons processed by the offset setting section to draw the three-dimensional map by perspective projection viewed from a specified viewpoint position and in a specified gaze direction, wherein the offset setting section shifts the first polygon and the second polygon to increase the height difference at a distant point from the viewpoint in the perspective projection than a close point to the viewpoint.