Hi,
today I played around with aerial images - they can be easily
overlayed for color filter spectacles for stereo viewing.
In future I could imagine that GRASS gets stereo measurement
capabilities...
http://WWW-Seiten/users/neteler/stereo/welcome.html
Find on that page some examples for you 3D spectacles from
SPEARFISH dataset.
Best wishes
Markus Neteler
neteler@geog.uni-hannover.de