Thanks for posting your source Lewil, I will see how fast it runs compared to my source.
In answer to refractor, yes it's polygon based. The terrain height map is generated & I make a little mesh for each point. I'm sure I will find lots of improvements in the next few months. I will track down the article if I don't have it. I think I downloaded most anything to do with terrain but don't remember the title.
I need to use an existing 3D engine as my maths is very poor so I can't just change the system but I'll see have a look see.
