Elevation data are a critical element in geological studies. From geological mapping to modeling earth systems and processes, geologists need to understand the shape of the earth's surface. Interpretations derived from images viewed stereoscopically are often superior and made with greater confidence to those from a single image. It is therefore advantageous to make use of satellite stereo pairs wherever possible. Most Earth observing satellites acquire images from a fixed geometrical perspective, which precludes stereoviewing. Satellite imaging systems that are able to acquire images from at least two different viewing angles can be used for stereomapping and for generating digital elevation models (DEM).
Vast amounts of digital elevation data exist, from large-scale global to smaller scale regional datasets, and many datasets have been merged to improve scale and accuracy. Decisions regarding which data to us for particular application, are driven by cost, resolution and accuracy. Content on this website shows the current status of available digital elevation data and illustrates the key applications. The types of data used include ASTER stereo satellite imagery and Shuttle Radar Topographic Mission data. Applications covered include: microclimate studies, delineation of drainage basins and their morphometric parameter, neotectonic processes, mineral and groundwater exploration, landslide investigations, meteorite impacts and other geological hazards.
Cross-Eyed Stereo View
In cross-eye stereo viewing the image for the left eye is on the right and the image for the right eye is on the left. You stare at a point about 1/2 way to the screen so that your eyes' gaze is crossing at the half way point. Thus the left eye sees the correct image which is on the right. As you cross your eyes the image will go double. When your eyes are properly crossed, you will see three pictures. The middle image will be in 3D, while the two outer images will remain in 2D.
Try to cross-eye view the image below:
Hints: There are several tricks that may help you as you learn. One is to move well back from the image you are trying to view. This will reduce the angle that your eyes need to converge at.
Another is to hold up a finger or pencil in front of the image about 1/3 to 1/2 way to the screen or printed image. Look at the pencil but concentrate on the doubled images on the screen. Move the pencil closer or further until they overlap to produce three images. The center one should be 3D, but out of focus. Then you need to shift your focus onto the center image without having it jump back to 2D (the tricky part :)
Another trick is to cut a square hole about the size of the image (the left side, say) in a sheet of paper. Hold this about half way between your eyes and the screen, centered between your eyes. When done properly it allows each eye to only see its own image. Removing the distracting extra images can help during the learning process.
Success: When the sample image is in 3D you will see the frame around the picture as the nearest thing (called the stereo window). The tree on the left is behind the stereo window but the closest object in the scene. The tree on the right is next further back. Then is the house and furthest is the sun.
Caution: Cross-eye viewing uses your eye muscles in ways you aren't (yet) used to. If your eyes begin to get strained, take a break and try again after some time.