HMP 
{
  12B: zeros
  4B float: always 0x3f000000 (0.5)
  4B float: terrain height scale 
  4B float: always 0x3f000000
  2B int  : tile count
  2B int  : ?
  4B int  : offset to tiles
  4B int  : offset to some data?
  2B int  : width in BLK
  2B int  : height in BLK
  array[width * height] of 2B int: tile indices 
  xB ?
  array[tile count] of TILE
  2B 0x0000
}

TILE [30B]
{
  2B int: texmap idx (from texture index file)
  1B int: ?
  1B int: lo - minimum height in tile (probably for terrain LOD? clipping?)
  1B int: hi - maximum height in tile
  array[25] of int8: 5x5 height values
}