SEARCH QUALITY METHODOLOGY AND PARTICULAR FINDINGS FOR KEY POINTS BASED ON MATERIALS OF OPTICAL-ELECTRONIC AERIAL SURVEY

Subject of Research. This paper presents the findings of the Scale-Invariant Feature Transform method for key points search. The method is used for the problems of photogrammetric processing of terrain images obtained from aircrafts and satellites. Method. The chosen method is widely used for spatial linking of images, tracking of changes and searching for objects, building of digital models and terrain orthophotoplans. The relevance of the Scale-Invariant Feature Transform method analysis lies in the fact that it was originally developed as a universal method for image processing in the field of technical vision. The existing modifications of this method, specialized for processing of terrain images, are applied in practice to a limited extent and have been studied without complete account of the image properties. In particular, the existing studies do not take into account the effect of the depicted plot on the key points search quality, which, in the general case, is characterized by a random combination of terrain objects. It is assumed that the plot features on the terrain image can cause significant variations in the distribution of the selected points in the image of a separate exposure when applying of the key points search method. To determine the dependence of the search quality for key points on the depicted plot, it is necessary to develop a methodology based on the features analysis of the Scale-Invariant Feature Transform method implementation and the use of a reference image set with various plot composition. As a content analysis result of the Scale-Invariant Feature Transform method, the criteria and rejection parameters of the determined key points are defined. The approach to the analysis of the image plot effect on the key points quality is based on the set of images classified by the characteristics of the plots on homogeneous and heterogeneous images. According to the proposed technique, the analysis is performed on the basis of the statistical and spatial distributions of key points obtained from individual images and their aggregates. Main Results. The research proposes a methodology for the dependence of the quality of the key points search result on the plot in the image. As a result of the experiment, factors are identified that cause a uniformity violation of the key points spatial distribution with the standard criterion for rejection of the key points. Practical Relevance. The results obtained make it possible to substantiate the need for development of a plot-oriented approach to terrain image processing by the key point search methods. The reason is that in order to perform and refine the spatial image linking, it is required to ensure the location uniformity of the key points used as control or joining points. It is revealed that the location density violation of the key points can be determined by the uneven image quality over the frame field. This phenomenon is associated, in particular, with different image sharpness in the central and peripheral zones.