MICRODEM Viewshed Algorithms
|Radials, full coverage (MICRODEM default)||The fan is drawn on another bitmap, and then merged onto the map. The map will show through. The program draws a number of radial lines, the number of radials being selected so that they overlap at the edges of the map and achieve complete coverage at the map scale. Points near the observer are calculated extremely close together, but the extra effort is worth it because the alternative is much slower.||
|Radial Lines, discrete||Draws series of radial lines away from the observer. Select ray spacing in degrees, and spacing of points along each profile to compute. At each point the intervisibility is computed, and drawn on screen. If the spacing for computing exceeds the pixel size you will see voids, and if the spacing is less than the pixel size, several computed points will plot on the same pixel. The fan is drawn over the map, and the only way to see the map is through the radials. This algorithm is the fastest of the three, but probably only if you do not go for full coverage.||
|Point to point||Fan is drawn on another bitmap, and then merged onto the map. This algorithm computes point to point intervisibility for every point on the screen and the observer. If screen pixel size is less than DEM spacing it will miss points, and for best accuracy you should blow up the map to 1:1 resolution. For large fans this can be very slow.||
Mixed pixels on fans.
Last revision 8/24/2017