Stereoscopy (3D vision) is fun, and maps are also fun. Therefore, stereoscopy + maps = even more awesome!
Remember Magic Eye 3D? As a kid I didn’t “get it” for a very long time, and it was frustrating to look at those crazy dots without seeing anything. But the moment your eyes click into the right place is immensely satisfying. Magic Eye is an example of autostereograms. The Wikipedia page gives a very detailed and understandable explanation of how they work and how to make them, so I won’t go over that here.
Briefly, when you view the rows of repeated images cross-eyed or wall-eyed, you are overlapping the adjacent images. The difference in the repeat period between rows gives the effect of depth. What if the adjacent images themselves were also stereoscopic? Then you would see an array of 3D images popping in and out! A 3D effect on top of a 3D effect. And what’s more – with globes.
for i in 60 30 0 -30 -60; do for j in 0 5 10 15 20 25 30 35 40 45; do gmt pscoast -Rg -JG$j\/$i\/3i -Bag -Dc -A5000 -Gwhite -SDarkTurquoise -P &amp;amp;amp;gt; globe_lat$i\_lon$j\.ps ps2pdf globe_lat$i\_lon$j\.ps globe_lat$i\_lon$j\.pdf rm globe_lat$i\_lon$j\.ps done done
I then arranged the little globes in rows corresponding to different latitudes, and columns corresponding to the longitudes (did this manually in Inkscape, but I’m sure that someone with more skillz could write a script for this too). A five-degree difference in longitudinal angle of view (between adjacent globes) is just right for stereoscopy. If the difference is too large (I tried 20 at first), the images don’t overlap well enough for the stereoscopic effect.
The spacing of the globes within each row was then slightly altered relative to each other, so that the rows would appear to “pop out” from the page at different depths. A grid background was added to make this even more obvious.
As a comparison, here’s one where the globes are flat, i.e. the adjacent globes in each row are simply the same picture repeated over and over, so there is no 3D effect of the globe itself, but you still have the Magic Eye effect of the rows popping out relative to the background.
If this gives you ideas for making your own autostereograms I’d love to hear from you in the comments below.