FROM DINOSAUR TRACKS TO DAM FACES: A NEW METHOD FOR COLLECTING THREE-DIMENSIONAL DATA

Close-range photogrammetry is an established method for capturing detailed information about a natural rock face or similar surface. Close-range techniques apply the same principals as do traditional aerial photogrammetry and allow for precise measurements to be made from photographs. For these measurements to occur, two major requirements must be met, complete coverage by overlapping photographs for stereoscopic viewing, and adequate x,y,z control for defined points within the overlapping area of the photographs. For traditional aerial photogrammetry projects the x,y,z control data is gathered through established surveying techniques or, more recently, by high accuracy Global Position System. Conventional ground control collection methods, when conducted with care, can obtain accuracies in the sub-centimeter ranges. These accuracies, although adequate for aerial photography at scales of 1:1500 or greater, may not support detailed close-range photogrammetric applications where highly detailed morphometric data is required.

Over the past six years research conducted at paleontological and archeological sites in Colorado, Wyoming, and Utah has employed the use of close-range photogrammetry to document, in three dimensions, subjects such as dinosaur tracks, dinosaur bone beds, petroglyphs, and rock shelters. Stereoscopic images of these subjects were analyzed utilizing both softcopy and hardcopy stereoscopic instruments, which have analytical capabilities to a sub-millimeter level thus, rendering conventional ground control methods inadequate for properly controlling the close-range subject to the needed level. Recent advances in affordable digital cameras and computer software that quantifies the distortions of these cameras has elevated the camera from simply a device for capturing images to a virtual surveying instrument. The techniques developed to photographically document and analyze Jurassic dinosaur tracks are being refined to assist in the evaluation of concrete dam faces.