Feature Request: surface cutaway: separate alpha chan?

[selden]

One of the movies recently made available on the Mars MOLA site is a rotating globe of Mars showing the surface partially cut away to reveal the Moho image of mantle thickness. As Mars rotates, the curaway region stays at the same position relative to the viewpoint. As a result, one can see how different surface features are related to the deeper structure of the planet as the planet rotates.

See http://svs.gsfc.nasa.gov/stories/MOLA/

Celestia can display a cut-away image, but only with the cut-away at a particular location relative to an object's surface features.. This is done by making a "cloud layer" image file that contains the object's surface texture plus an alpha channel to make an area transparent.

Here's an example:


In order to implement a "rotating cut-away", however, the transparent region (alpha channel image) has to change locations relative to the image that it's associated with. It'd be really nice if Celestia could do this somehow.

Added later: the png file that I used for this cutaway is available on one of my Gallery pages: http://www.lns.cornell.edu/~seb/celestia/gallery-002.html#8


Note that it's almost 3MB..