heightmapWidth and heightmapHeight always equal

heightmapWidth and heightmapHeight always equal, can’t it not equal? i have a dem data which has 1013 columns and 980 rows, and i wanna to set terrain’s resolution to 1013*980 so that 1 unit equals to 1 meter, why heightmapWidth and heightmapHeight can not set to different value?

Sadly, I have read that you can't make a non-square heightmap. The only valid solution I saw was to create a simple wrapping function that returned a heightmap coordinate, calculating from the source map coordinate in the fashion of a simple x / y factor of percentage between the two resolutions.