Overlaying inline images

Bob Kanefsky (kanef@ptolemy-ethernet.arc.nasa.gov)
Thu, 17 Nov 94 21:54:19 PST

Some of the planetary scientists here have been asking me to extend my
Mars Atlas (http://ic-www.arc.nasa.gov/ic/projects/bayes-group/Atlas/Mars/)
to include optional overlays, so that coutour lines, place names, or both
can be displayed on top of the image maps. With the current version of HTML,
that can only be done by having four sets of images (one plain, one with
contour lines, one with place names, and one with both). If N overlays are
available instead of just two, it quickly becomes infeasible, requiring 2^N
sets of images. (In theory the server could run a script to combine them, but
that isn't feasible here, and it would be very CPU intensive.)

Is there any chance that browsers in the future can be made to accept some
kind of overlay markup, specifying that two or more transparent GIF images of
the same size and shape should be displayed one on top of another as one
inline image?

It would also be nice to have a similar syntax that specifies that the first
image should be displayed by itself, and a control should be inserted next to
it that flips to the next image. This would be useful for flipping between
visible and infrared in an orbital image, skeleton and muscle in an anatomy
drawing, and so on. I'm not suggesting inline MPEG capability (which would
soon tempt every organization to have a flying logo on its home page). Each
frame would be a separate file (probably GIF), and the second frame need only
be downloaded if the user requests it.

-- 
				      --Bob Kanefsky (Recom Technologies)
					Computational Sciences Division
					NASA Ames Research Center