[Proj] Point Scale factor service
bfraser at geoanalytic.com
Wed Apr 21 13:39:01 EST 2010
Lately I've run into issues regarding scale. The need to:
- measure a distance on a web map application
- show layers based on map scale
In the past, I've carefully selected a good projection (and parameters) to
minimize these problems. These days, the standard is Spherical Mercator (thank
you Google), and most applications ignore the map projection's point scale
factor at the location/view of interest, or do their own hack to estimate it.
I thought a more robust solution would be to have a function in proj to
return the point scale factor at a location, something like:
int pj_pointscale( ProjPJ prj, double lon, double y, double *pointscale );
(return FALSE if not available for that projection?)
The calling applications could then do something useful with that information.
More information about the Proj