TABLE OF CONTENTS Photogrammetry has established itself as the main technique for obtaining precise 3-D measurements from stereo overlapped imagery. Conventional photogrammetry involves the use of expensive plotting equipment to mimic the stereo geometry (stereo model) at the moment of image exposure. This is accomplished through two steps: (1) the inner orientation that establishes the relationship between the camera space coordinates and the model space coordinates through the use of either fiducials or reseau marks, and (2) the relative orientation process that establishes the correct position and orientation of one photograph relative to the adjacent overlapping photograph. This is achieved by enforcing the condition that conjugate rays intersect. When relative orientation is complete the so-called photogrammetric model is established (Shears and Allan, 1996).
Once oriented, all residual y-parallax will have been eliminated, allowing the operator to view the model in stereo. The last step is to relate the model coordinate system with the ground coordinate system through the absolute orientation process. Absolute orientation is the process of solving the orientation elements, which relate an arbitrary system of coordinates (the model system in our case) to the reference system (the ground coordinate system). The absolute orientation is done analytically with the help of model and ground coordinates of a minimum number of two planimeteric and three height (i.e., with known X, Y, Z in both systems) control points.
Once the model has been absolutely oriented, it is possible to extract the DTM...
