ON LOCATION Introduction In the Field Back in the Lab What We Can Learn Back in the Lab Using photogrammetry, scientists can create a stereoscopic (3-dimensional) image. Neffra Matthews uses an analytical stereoplotter to combine the information she gathers in the field to create accurate three-dimensional images of the tracks. This is achieved by creating a series of overlapping photographs or perspective views. Very reliable measurements can be taken from these photographic images if the following conditions are met: a) stereoscopic images cover the entire object to be analyzed, and b) the x, y, and z (width, height, and depth) coordinates are known for at least three points in the overlapping photographs. By using a piece of equipment called an analytical stereo plotter, Neffra is able to combine the aerial photographs with the ground-control coordinates to create an accurate three-dimensional view of the tracks. Through the viewer she can see two overlapping photographs at the same time and match them to the ground points. A map that matches what is actually on the ground is created by plotting the entire series of photographs. The equipment also allows Neffra to digitize and transfer the high-resolution images to a personal computer for further study. NEXT: What We Can Learn