Stereoscopic Images - Geology in 3D

Stereo photos allow human eyes to turn two flat images into a three-dimensional view. Mappers work with stereo aerial photos using viewers. But geologists learn to view stereopairs without a viewer.

Practice on these examples. The basic technique is to cross the eyes so that the two images overlap completely. At that point the brain "locks in" on them and a 3D scene appears.

Start with your monitor square and centered, with the stereopair directly in front. Hold a fingertip in front of the images and focus on it, then bring the finger toward your nose while staying focused on it. As you do so, notice the stereo images behind it overlapping more and more. When they fully overlap, carefully direct your gaze to them without changing the direction of your eyes, and the 3D image should appear. For the 500-pixel images, your finger should come halfway to your face. For the full-size images (click on the smaller ones), your finger should come about three-fourths of the way to your face.