Great, thanks guys.
I actually started working on some improvements to the code, mainly for efficiency (in terms of framerate) which happen to include building the mesh out of multiple GeomPrimitive’s anyway. The mesh is so big (I’m now scaling it to 10 or 100 times the size it was in the currently released code, that’s scaling, not increasing the no. of triangles) that it can’t all fit on screen at once, so it is not the most efficient thing to have the whole mesh as one GeomPrimitive, even regardless of this index error.
So, it may be that the current development version I have can handle much larger height maps, I’ll try it sometime.