getHeightmapData question

The values of the heightmap are floats. Are these values within range [0.0 - 1.0]?

Meaning if the heightmap was represented by a 16 bit .raw image, 1.0 would be 65536, and 0.0 would be 0?

That's correct (except that the maximal value for a 16 bit unsigned integer is 65535 ).