The article describes theoretical and practical issues of evaluation of the actual resolution of digital aerial and satellite imagery using an edge profile curve. As a measure of resolution, a linear resolution element, is defined as the minimum width of the image separate linearly extended object is still detectable in the image. The edge for the purposes of estimation a digital image is defined. The theoretical part of the article is devoted to the description of the method for estimating the resolution of an image using an edge profile curve and a fast Fourier transform. An algorithm for automatically estimating the resolution of digital photo images along an edge profile curve is presented. Terms of selection of an edge in a digital image area are defined and an algorithm for automatically finding edges in the image that meet the specified conditions in the best way is developed. A method for automatically extracting edge profile curve from a digital image is described for the following evaluation of the resolution. A method and algorithm for the transition from pixel values of the edge profile curve to the frequency-contrast characteristic of a digital image is described. The results of an experimental accuracy estimation of determining the resolution with the method using the proposed algorithm are compared with the results obtained visually by the resolution test chart. The examples of the results of evaluation of the actual resolution for various aerial and satellite imagery are presented.
The article shows the relevance of numerical evaluation of digital aerial and satellite images’ contrast as one of their main characteristics, which is important for photointerpretation. The formulae for expressing the numerical values of the contrast from a variety of sources are presented and analyzed. An example of images and their contrast with different formulae clearly show the inadequacy of the estimates of the contrast for some of the formulae and it allows you to select the most appropriate mathematical expression of the contrast. Enhancements to expressions numerical parameters for an evaluation of the contrast of the digital image were proposed. One of the proposed formulae is appropriate for general evaluation and another one for the assessment of local contrast, which can also be used to assess the effectiveness of the use of the entire scale of possible brightness values of the pixels, i.e. the bit of the digital image. Examples of evaluation of using these formulae were given.
The authors present the results of certification testing software-and-hardware complex on the basis of an unmanned aircraft (UAV) “Geoskan 401”, designed for aerial mapping. The substantiation of the need to assess the accuracy characteristics of the photogrammetric processing aerial photos results from the UAV is given. The composition of the complex, the parameters of the test site and the performed aerial photography are given, the order and method of testing are described. Assessment of the aerial triangulation accuracy, creation of a digital elevation model, digital orthophotos and coordinates of marked and unmarked characteristic points (natural contours) of land boundaries and building contours were carried out to confirm the compliance with the requirements of regulatory documents for the implementation of photogrammetric processing, maintenance of the state real estate cadastre and surveying. The values of the spatial data accuracy obtained with the help of a hardware-and-software complex confirm the possibility of using the “Geoskan 401” in real estate cadastre and surveying. Recommendations on the use of hardware and software complex for cadastral and mine surveying works are given.
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