Michael wrote: > What needs to be done IMHO is to figure out what a 1:1 > horizontal/vertical ratio should be for any map and set that > to 1 in the z-exag slider. BUT, we need to decide what a 1:1 > ratio really is. This is easy for a projected DEM. Using > grass libraries, it should be pretty easy for a latlon DEM > too.
exactly 1852m in a nautical mile. exactly 60 nautical miles in a degree latitude. that gives a basic meter to degree conversion for the map, BUT it is not guaranteed that the DEM data is in meters, not feet or anything else. r.support/r.info units= was added to record this, but it is a freeform field so you can make it micro-Einsteins per m^2 per sec, \mu and all, or whatever, so can only be used as a hint if it is there and matches a known list. tcltk nviz has a hack to support that, but it isn't fully implemented, e.g. the lighting is still quite wacky for that. theoretically for regions smaller than say 3 degrees in EW extent lat/lon we might look at skewing the aspect ratio for cells by 1:cos(lat_center) to reduce the distortion. very crude but fast and passable as a first order correction for something which is for visible purposes only. or just display an error message saying you should try to use a projected location instead. Hamish _______________________________________________ grass-dev mailing list grass-dev@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/grass-dev