File of TAB format is a text file which contains description of features of different spatial categories. To import raster data TAB files containing description of image features are used.
Description of an image feature includes the name of file of one of graphic format in which raster graphics are stored and a list of control points. Every point contains two pairs of coordinates, one pair specifies position of the point in map coordinate system, the other one determines the point (pixel) of raster image stored in the file. The number of control points of the features should not be less than three.
When performing import of image feature to selected feature type of ObjectLand map georegistration of the feature to the map by specified control points is performed. For georegistration of image features see chapter 17 “Adding and editing features”, subsection “Adding and editing image features”. If the number of control points is more than three, the method of least squares is used to minimize deviation of coordinates of control points georegistration.
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