You are using the wrong command. You seem to be using the Advanced Terrain commands in which case you need to use
get terrain ground height
From the free Help files provided by Sixty Squares (I think
):
Quote: "GET TERRAIN GROUND HEIGHT
Returns the height of the terrain at the given X and Z coordinates. It's just like the GET GROUND HEIGHT command for a matrix, but it's for Advanced Terrain.
Syntax
return float = GET TERRAIN GROUND HEIGHT( Terrain ID, X, Z )
Related Information
RETURN TO COMMAND LIST
Example Code
Advanced Terrain Original Example (HTML Preview)
Advanced Terrain Original Example (.DBPRO)
Advanced Terrain Simple Example (HTML Preview)
Advanced Terrain Simple Example (.DBPRO)
"