The origin of ground photogrammetry

19 1 1 year, Germany made a relatively perfect ground stereo mapper designed by Austria ohrel. This surveying and mapping instrument is mainly composed of a three-dimensional coordinate measuring instrument and a plane and elevation intersection bar. Its structural principle (Figure 3) is to decompose the spatial projection ray formed by two photos P 1 and P2 into two parts: one part is projected on the XY plane of the rectangular coordinate system in the object space. When the coordinates of stereo observation photos are one of x 1, z 1 and x2, the forward intersection is indirectly realized by the directional rod L 1 of the left photo projection center S 1 and the parallax rod L2 passing through the right projection center S2, and the plane position of the ground point is determined. At this time, S 1S2=B, where b is the baseline value expressed in the drawing scale. The other part is projected on the YZ plane of the object, which is represented by the elevation bar H 1. Because the Y coordinate of the measured point has been determined by plane intersection, the elevation of the point can be determined only by using the left elevation bar H 1. The structure and principle of all kinds of ground stereo surveying and mapping instruments produced in modern times are basically the same as those originally created by ohrel, but some improvements have been made. For example, adding a right elevation pole automatically eliminates the up-and-down parallax during observation; Some are also equipped with tilt calculators to handle equal tilt photography. Some stereo mappers, which are mainly used in aerial survey, can also be directly used to process the image pairs of ground photography.