Attempt to compute height map metadata, loading assets as required. NOTE: if the heightmap pixel represents a quad in the terrain geometry in the exporting program, the geometry produced here is slightly different, with the border slightly clipped, and the terrain and quad size, slightly larger. i.e if the original map is 32m^2 and the original quad 1m^2 and the heightmap is 32x32, the quad axes below will be > 1.0.