What are the methods of aerial photogrammetry?

There are three methods of aerial photogrammetry, namely, comprehensive method, all-around method and division of labor method (or difference method).

1. aerial photogrammetry synthesis method is a mapping method combining photogrammetry with flat panel measurement. On the topographic map, the plane position of ground objects and landforms is obtained through photo correction, and the elevation and contour lines of topographic points are measured on the spot by ordinary measurement methods. Suitable for large-scale mapping in flat areas.

2. The universal method of aerial photogrammetry is based on the principle of geometric inversion in the process of photography, establishing the geometric model of the ground in the stereo plotter and drawing the topographic map. When placing photos on the stereo mapper, the purpose is to make the restored projection beam similar to the photographic beam (the projection beam can also be changed under certain conditions). Because no control points are added in the process of relative orientation of image pairs, only the inherent geometric characteristics of image pairs are used. The orientation of geometric model is arbitrary and the scale of model is approximate, so the map can only be measured by absolute orientation.

3. The division method of aerial photogrammetry (difference method) is a mapping method based on the principle of plane and elevation division. The main instrument used is stereo measuring instrument. It is an instrument to measure the left and right parallax according to the vertical photographic image pair, and draw contour lines on the right photo. The difference of abscissa x of a ground point in the left and right photos is called left and right parallax p, while the difference of left and right parallax of two ground points is called left and right parallax comparison Δ p, which is caused by the height difference between two points. In the process of measuring the left-right parallax ratio Δ p, with the help of the correction components on the instrument, the influence brought by the external orientation elements of photography is automatically corrected to make it equal to the left-right parallax or the left-right parallax ratio of the ideal image pair; The elevation difference is calculated by the elevation difference formula; Then, the contour lines outlined in the photo and the ground objects drawn are projected by a projection plotter and drawn into topographic maps in different areas. The X-2 parallax mapping instrument designed and manufactured by our country is based on the stereo measuring instrument, and the plane correction part is added. The improved instrument can solve two steps in division of labor drawing at one time, which improves the work efficiency. Italy and the Federal Republic of Germany have similar instruments.