GTOPO30Options Enumeration

Uses the upper-left coordinates described in the ULXMAP and ULYMAP fields in the terrain format, rather than rounding the tile coordinates to whole degrees.

GTOPO30 terrain data is typically distributed as multiple tiles, each of which describes a rectangular region of the Earth. The coordinates of these rectangles can be described in whole numbers of degrees. For example, the W180N90 tile covers the rectangular area from -180 degrees to -140 degrees longitude and from 40 degrees to 90 degrees latitude. These coordinates are not directly specified in the header file, however. Instead, the ULXMAP and ULYMAP fields describe the coordinates of the center of the northwest cell, and the XDIM and YDIM fields describe the size of each cell. From these fields, the northwest corner of the rectangle can be computed. However, due to rounding error in these fields, the intended whole numbers will not necessarily be computed precisely. For that reason, by default, the GTOPO30Terrain provider rounds the rectangle's coordinates to the nearest whole numbers. Setting the StrictlyHonorUpperLeft option disables this rounding and uses the values computed from the terrain data file.