Significance and premise of multi-slice forward intersection

The significance and premise of forward intersection: the method of observing the horizontal angles of fixed points at two or more known points respectively and calculating the coordinates of fixed points according to the coordinates of known points and the observed angle values. Rear intersection: a method of observing the horizontal angles of at least three known points on the point to be fixed and calculating the coordinates of the point to be fixed according to the coordinates of the three known points and two horizontal angle values. The definition of spatial rear intersection is a method to determine the external orientation elements of a single image by using ground control points and their image points on the photo. If the six external orientation elements of each photo are known, the relationship between the photographed object and the aerial photo can be determined. Therefore, how to obtain the external orientation elements of photos has always been a problem discussed by photogrammetry workers. At present, the measurement methods used are: using radar, global positioning system (GPS), inertial navigation system (WS) and on-board camera to obtain the external orientation elements of photos; Photogrammetry can also be used to measure the intersection behind the space.