SU741051A1 - Method of automatic recognition of identical points on stereocouple photographs - Google Patents

Description

one

The invention relates to the field of photogrammetry.

The known methods for identifying points consist in scanning each of the two photographic images, converting optical densities into electrical signals, and determining the amount of non-displacement of points by processing the signals.

A known method for electrical correlation signal processing, in which one-dimensional optical correlation is used for image correlation analysis (identification). However, experiments on its use did not yield positive results.

There is also known a method consisting in scanning each of two stereo pair images, converting optical densities into electrical signals, and determining the parallax shifts of image points using the correlation dependences 1 obtained.

A disadvantage of the known methods is the unreliable identification of points in areas with a uniform photographic image structure (heavily forested terrain, water surface, etc.), flat homogeneous terrain areas.

The aim of the invention is to increase the reliability of identifying points on homogeneous sections of photographic images. 5 The goal is achieved by placing a second, having identical sections onto one of the images before scanning, turning it in its plane, and simultaneously scanning a pair of conjugated images around one

The 10 points selected on one of the images convert the optical densities into an electrical signal, then the differential movements of the other image relative to the first align the center of the resulting moire pattern with the selected point, controlling the alignment process with the electrical signal.

The method is based on the appearance of a moire effect, detected when two stereo pairs of the same name are superimposed on each other.

20 with pictures of uniform areas: forest, water surface.

Claims (2)

FIG. 1 and FIG. 2 shows photographs of the forest and water surface, respectively; in fig. 3 and FIG. 4 - photographs of the moire effect that occurs when the corresponding images are superimposed on each other; in fig. 5 is a diagram explaining the method. The moire effect arises when mating (optical or direct imposition on each other) of two identical photographic images or zones of the same name of a stereo pair and turning one of the images at a small angle, in the order of 1-10 °. The moire effect zone has a circular shape with a center at the point of mutual reversal of images; diameter depends on the angle of the image. The moire effect is a visualization of the two-dimensional autocorrelation function of images of like-named K () iSST, C, y) -TaCx 2 y | dxdy, gdet (J :, y) and Tb (l; -1- (2, y + t) are photo image transmittances. The maximum of this function corresponds to the center of the moire effect zone and the coincident identical points of two photo images. The proposed method of identifying identical points differs from known, based on correlation processing of electrical signals, using a two-dimensional optical correlation between photographs and the use of the detected moire effect. Fig. 5 is a diagram explaining the method. .. Of 2. At points B C t) belong to the first image, Aj, B j, € 4 - second. Concentric circles show a moire pattern that appears at point А 4, which coincides with point Aj. The process of identification is as follows. Let point B be selected in image 1. When moving image 2 in the direction (the moire pattern moves along line I and its center is located at point B, when this point coincides with identical point B a- In general, when the direction of movement does not coincide with one of the axes of the rectangular coordinate system X , Y, differential (separate) image movements are necessary. 2. The magnitudes of these displacements can be used to determine the parallax of points B1 and B a. The technical solution of the problem of combining the center of the moire effect with the selected point is possible with known technical means, since the zone of the moire effect, which has a circular shape, differs from the neighboring zones. When scanning around point B, for example in mutually perpendicular directions, the shape of the electrical signal will be symmetrical about the center of the scan (point BI) when the center of the moire pattern moves to point B.i. In all other cases (if the scanning center and the center of the moire pattern do not match), the shape of the electrical signal will be asymmetric. Thus, the method of automatic identification of identical points on stereopair images consists in the following sequence of operations: one of the images is rotated, for example the second in its plane by an angle of up to 10 °, and a moire pattern appears around arbitrary points of the same name; scanning a light beam simultaneously of a pair of superimposed (conjugated) images around a point selected on one of the images (for example, around point B i) using optical converters to convert optical density of images into an electrical signal; differential movements of the image 2 move the center of the resulting moire pattern to the selected point, controlling the process of combining the center of the moire pattern with the selected point using an electric signal, achieving its symmetrical shape relative to the center of scanning (selected point). The invention provides reliable identification of points in areas with a homogeneous structure of photographic images (forest, water surface) representing a statistically homogeneous (or quasi-uniform) random field. The moire effect instantly arises when mating photographic images and, without destroying, moves as one of the images moves, with its center corresponding to identical points. The emergence of a moire effect depends only on the nature of the structure of the photographic image and the size of the area. Claims The method of automatic identification of identical points on stereopair images by scanning them, characterized in that, in order to increase the reliability of identification of points on homogeneous sections of photographic images, before scanning, the second one having identical sections is rotated in one of the images in its plane, scanned one beam at the same time a pair of conjugate images around a point selected on one of the images, convert optical densities into an electrical signal, then g fferentsialnymi movements of the other image relative to the first combined center resulting moire pattern with the selected point, the process of controlling the alignment with an electric signal. tiv vi 5; i: -, f--; V 4 th :,  S, - -. . .-, women, - -: J 1G . - “i, - - g- :. .: h- v: - .; 4: x ::%: 4-v: -, - 7-- -J--. , -r -v -: - --- IV- -: / - Sources of information taken into account during the examination 1. The book “Manual on photogrammetry, trans. from English “Nedra, M., 1971, p. 19-27. FIG. one (VM i.,. FIG. 2 fe.