[Xastir] [tiling] reading tiles slow

[Tom Hayward]

> Note that for the USGS topo (UTM projection) map code we did NOT
> reproject the map, instead going for "good enough" map reprojection
> with custom code focusing on speed.  The resulting 7.5' quadrangle
> pixels may be off from their true position by a small number of
> meters as a result, but they render very quickly in Xastir.  The
> 1:100k and 1:250k maps are not as well positioned, but they're also
> not anywhere near as detailed.

Ok Jerry, how hard would it be to skip the projection for high
layer-number tiles (the close zoomed-in ones)? I assume the projection
difference is minimal there, so it would be worth a pixel different
for the faster render times.

Tom