I once experimented with something like this for OpenXcom is to first rotate the geographic coordinate system so that local equator/zero meridian intersection i

I once experimented with something like this for OpenXcom is to first rotate the geographic coordinate system so that local equator/zero meridian intersection is at the center of the area of interest, then apply merkator or whatever other projection you like. Otherwise it's a sea of hacks which doesn't get rid of latitude-induced distortions anyway. After that being very annoyed with lat/long stuff I moved to N-vector representation. https://en.wikipedia.org/wiki/N-vector https://en.wikipedia.org/wiki/N-vector