colliding fast moving objects? position in last frame

hi i read someplace on this website that it help to collide fast moving objects if you cast a ray from the position of the object this frame and the last frame. and if the ray hits something then move the object back to the position on the last frame. so i was wondering how to get the position of a object in the last frame.

thanks.

You can't - what you need to do is store the position yourself each frame

Check out the DontGoThroughThings script on the wiki, it does exactly what you want:

http://www.unifycommunity.com/wiki/index.php?title=DontGoThroughThings