Describe the operation process of aerial photogrammetry.

Aerial photogrammetry refers to the operation of continuously taking photos on the ground with aerial photographic instruments on the plane, and drawing topographic maps in combination with the steps of ground control point measurement, mapping and three-dimensional mapping.

The basic principle of aerial photogrammetry is perspective transformation of central projection, and the basic principle of stereo mapping is geometric inversion of projection process. The work of aerial photogrammetry is both outdoor and indoor. The field work includes: ① Joint survey of photo control points, which are generally landmark points laid on the ground before aerial photography, or obvious feature points in photos (such as road intersections), and their plane coordinates and elevations are measured by common survey methods such as angle intersection, ranging traverse, contour leveling and elevation traverse. (2) photo adjustment, that is, by interpreting photos, drawing features, landforms and other elements with prescribed topographic map symbols; Surveying and mapping without images and new important features; Pay attention to the place names obtained through investigation. (3) Comprehensive surveying and mapping, using a flat plate to survey contour lines on a single photo or photo map. The indoor work includes: ① Encrypting the control points of mapping, generally using aerial triangulation, calculating the control points needed for mapping according to the control points of photos, and checking their plane coordinates and elevations. ② Measure the original topographic map.

The methods of drawing mainly include comprehensive method, all-round method and division of labor (difference method). Synthesis method is a mapping method combining photogrammetry with flat panel, which belongs to single photo mapping. According to the corrected aerial photograph, the plane position of the ground point is determined, and the elevation and contour line of the ground point are measured by the flatbed car. Suitable for large-scale mapping in flat areas. Omni-directional method is a method of putting stereo images in a stereo plotter to form a reduced geometric model of the ground, and measuring the plane position, elevation and contour lines of ground points on the stereo model to obtain topographic maps, which is mainly suitable for mountainous areas. Division of labor is a drawing method based on the principle of dividing plane and elevation. The elevations of ground points and contour lines are measured on three-dimensional surveying and mapping instruments. The determination of the plane position of ground points is the same as the comprehensive method, which is suitable for hilly areas.