The article is devoted to the problem of evaluating the detailing of spatial data. In geoinformatics, spatial data detailing determines how detailed a particular object is representeda map image, and the detail score allows you to analyze the permissible accuracy of spatial objects for a specific user task. An approach to the definition of detailing concept is proposed. The evaluation of the object’s detail depends on its characteristics: geometric, semantic, and topological. A study is being conducted to select the geometric characteristics of the object that reflect its detail. For linear objects, in addition to the characteristics of the line as a whole (length, number of points, sinuosity, average rotation angle), it is suggested to consider its smaller details, such as bends and triplets. A bend is a section of a line where the angle of rotation retains its sign. A triplet is a combination of three consecutive points. Based on the results of the study, the geometric characteristics that change in the trend depending on the scale were selected. The paper presents the developed software for assessing map detail—the MapAnalyser toolbar for the QGIS geoinformation system. The functional capabilities of the developed software are described. The toolbar allows you to get the geometric, semantic, and topological characteristics of a layer or set of layers, as well as to evaluate the graphical complexity of a map image based on RlE encoding. The program code is written in the PyQGIS language. The software has passed state registration and is hosted on the github server. With its help, new results were obtained on the evaluation of spatial data granularity. New software, embedded in QgIS, to assess the detail of the map and spatial data, based on taking into account geometric and symbolic (used in the display) parameters. The software allows to calculate the metrics of spatial data detail, as well as to assess the complexity of the cartographic image. It’s can be used in the integration of data obtained from different sources, assess the compliance of data detail and the map scale, to assess the complexity of the map for different purposes and scales.
In map production it is necessary to keep the spatial relationships between map objects. Generalization is the simplification performed on geographical data when decreasing its representation scale. It is a common practice to simplify each type of spatial objects independently (administrative boundaries first, then road network, hydrographic network, etc.). During the process some spatial conflicts, which require manual correction, arise inevitably. The generalization automation still remains an open issue for data producers and users. Many researchers are working to achieve a higher level of automation. In order to detect the spatial conflicts a refined description of spatial relationships is needed.The paper analyzes models of describing topological relationships of spatial objects: the nine intersections model, the topological chain model and the E-WID model. Each considered model allows to take into account some relations between objects, but does not allow to transfer them exactly. As a result, the task of developing a model of relations preserving topology is relevant. We have proposed an improved model of nine intersections, which takes into account the topological conflict that occurs when a point object is located next to a simplified line. Line simplification is one of the most requested actions in map production and generalization. When the mesh covered the map inside the cell there can be points, line segments and polygonal topological objects, which, if the cell is rather small, are polyline objects. Thus, the issue of simplification of topological objects within a cell is reduced to the issue of simplification of linear objects (polylines). The developed algorithm is planned to be used to solve the problem of consistent generalization of spatial data. The ideas outlined in this article will form the basis of a new index of spatial data that preserves their topological relationships.
The paper reveals dependencies between the character of the line shape and combination of constraining metrics that allows comparable reduction in detail by different geometric simplification algorithms. The study was conducted in a form of the expert survey. geometrically simplified versions of three coastline fragments were prepared using three different geometric simplification algorithms—Douglas-peucker, Visvalingam-Whyatt and Li-Openshaw. Simplification was constrained by similar value of modified hausdorff distance (linear offset) and similar reduction of number of line bends (compression of the number of detail elements). Respondents were asked to give a numerical estimate of the detail of each image, based on personal perception, using a scale from one to ten. The results of the survey showed that lines perceived by respondents as having similar detail can be obtained by different algorithms. however, the choice of the metric used as a constraint depends on the nature of the line. Simplification of lines that have a shallow hierarchy of small bends is most effectively constrained by linear offset. As the line complexity increases, the compression metric for the number of detail elements (bends) increases its influence in the perception of detail. For one of the three lines, the best result was consistently obtained with a weighted combination of the analyzed metrics as a constraint. None of the survey results showed that only reducing the number of bends can be used as an effective characteristic of similar reduction in detail. It was therefore found that the linear offset metric is more indicative when describing changes in line detail.
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