I could make another map file for the physics... Which is a regular grid...

You could use pointers to your vertices in the "squares" if you want to save some memory. But seriously even if you have a million vertices that would only amount to a few MB of ram.

Or yeah, use a regular grid if that's possible, it's much faster.

OK then Najdorf, I didn't realise. Thankyou lots Najdorf and everyone. I might use Skorche's Technique for projectile col.dec..