If the object was created with CreateObjectFromHeightMap then this command can be used to quickly get the height of the object at a particular world position. This accounts for the object's position and Y rotation to provide the height regardless of where the object is positioned. If the object is rotated in the X or Z angles then this will produce incorrect values. You should provide the X and Z coordinates in world units, if the point lies outside the object then 0 will be returned.
float GetObjectHeightMapHeight( objID, x, z )