Method of generating an elevation database

A method of generating a terrain elevation database for selected urban regions, the method comprising:

• (a) receiving a city atlas database, a rural-urban database, and an input terrain elevation database, the city atlas database containing location coordinates of cities in selected urban regions, the rural-urban database including rules for determining for which said cities corresponding bounding regions enclosing continuous urban regions are to be constructed;
• (b) for each location in the city atlas database for which, according to said rules from the rural-urban database, a said bounding region enclosing a continuous urban region is to be constructed:
• constructing said bounding region;
• (c) filtering the bounding regions by removing any bounding regions encompassing selected urban regions having a population lower than a minimum population size;
• (d) dividing each bounding region into mapping tiles;
• (e) removing from each bounding region any mapping tiles representing non-urban areas;
• (f) applying terrain elevation data from the input terrain elevation database to each bounding region, to produce a plurality of mapping tile elevation data files;
• (g) compressing the elevation data in the plurality of mapping tile files using the JPEG method of compression, wherein each mapping tile is compressed by adjusting the JPEG quantization factor to achieve maximum compression for a designated level of distortion;
• and
• (h) packing the plurality of compressed mapping tile data files by classifying MEG headers of the mapping tile files by header type, and by storing the header type instead of the header for each mapping tile JPEG file;
• wherein, upon decompressing the elevation data, each point in each tile represents a level of terrain elevation at that point in the associated selected urban region.