Real time digital map shading

摘要

A digital shaded map rendering method for assigning an illumination intensity to pixels in a video display of the map comprises the following steps: 1. providing a rectangular grid array of altitude values covering a map area to be shaded. The location of each altitude value has a map position characterized by a coordinate location referenced to a first and second coordinate axes crossing orthogonally at an origin. Each coordinate location has a first and second value. Each first and second value characterizes the distance of the respective coordinate location from the origin measured along the first and the second coordinate axis. 2. Dividing the map area into an array of contiguous polygonal areas. Each polygonal area has a perimeter bounded by straight line segments passing between at least three coordinate locations. The video display has pixel areas that corresponding to each respective polygonal area. 3. Calculating a normal vector for each polygonal area. 4. Providing an illumination vector referenced to the coordinate axes characterizing the direction and intensity I of a light source that illuminates each map area. 5. Calculating a relative angle between the normal vector and the illumination vector for each polygonal area. 6. Assigning a relative intensity to each respective pixel area in the video display, each relative intensity being a function of the relative angle. 7. Displaying an array of polygonal areas forming at least a portion of the map area in a video display. Modulating the illumination intensity of each pixel area to correspond to the relative intensity assigned to that pixel area.