Relative orientation refers to the restoration or determination of the relative relationship of image pairs in photography. The theoretical basis is the coplanar principle of homonymous rays. The relative position can be expressed in two ways:
(1) With the photographic baseline as the reference, it is expressed by the five angular rotation values of the image pair of two light beams, which is called the relative orientation of the single image pair
(2) Taking one picture as the reference, the other picture is represented by two linear movement values and three angular rotation values, which is called "relative orientation of continuous image pairs".
There are two solutions:
(1) Optical mechanical method. Using the angular rotation of the projector and the linear motion of the baseline support on the stereoplotter, the up and down parallax of at least five identical image points in the image pair is eliminated
(2) Analytic method: measure the coordinates of at least five points with the same name in the image alignment on the coordinate measuring instrument, and calculate the value of the relative orientation element according to the relationship between the relative orientation element and the upper and lower parallax. Complete the relative orientation of the image pair, that is, it can be considered that the free scale and the geometric model of the camera area at any position in space have been obtained, and the model at this time may be inclined.