Add-on post from the locked Rulers (http://www.lemmingsforums.net/index.php?topic=2961.0) topic.
The nx_sketches.dat is a very useful feature; however, they are missing the glider shadows.
I don't know how useful they'd be, nor how easy to implement - the simple parts of glider movements are easy enough to figure out, while the tricky parts (eg. bouncing off walls) would require more or less full simulation of their physics. Indeed, the whole reason shadows based on simulating the lemming fully were introduced into the game was to properly handle gliders; it was added later for other skills as a "if the capability is there, why not use it to improve accuracy" matter.