trying to modify Eric Haines TerrainObjExporter so that it writes a subset of the terrain

And I have two questions: How can I debug/printout variables for this code and what's wrong with the terrain.GetHeights call in the following code snipppet

 function Export () {
     var fileName = EditorUtility.SaveFilePanel("Export .obj file", "", "Terrain", "obj");
     var w = terrain.heightmapWidth;
     var h = terrain.heightmapHeight;
     var meshScale = terrain.size;
     var tRes = Mathf.Pow(2, parseInt(saveResolution));//1,2,4,8,16  ??
     print("w= "+w);
     print("h= "+h);`enter code here`
     print("tRes= "+tRes);
     meshScale = Vector3(meshScale.x/(w-1)*tRes, meshScale.y, meshScale.z/(h-1)*tRes);
     var uvScale = Vector2(1.0/(w-1), 1.0/(h-1));
     //var tData = terrain.GetHeights(0, 0, w, h);
     //w == h ??
     var tData = terrain.GetHeights((w/2)-20, (w/2)-20, (w/2)+150, (w/2)+150);

The print statement is not executed, or doesn't work in this context, and the error is thrown before any output.

Help much appreciated. Chris