triangle area not representative of curved GIS projections

[Permafacture]

It would be slow to use a projection dependent triangle area calculation. This would only matter for shapes that span a lot of latitude or longitude. If things were confined to planar or lat/lon, then lat/lon could make a rough correction by multiplying the area by cosine of the latitude of something? Also, VWSimplifier could take a triangle area calculating function as an argument, so in the rare case where you are working with shapes that do span a lot of latitude or longitude, one could use a slower but more accurate function.