Preparation of control points

At presence of analog photos it is required to put "pinholes" onto a photo and to sign numbers of points, i.e. it is necessary to specify location of control points in the analog photo.

At presence only of a source raster it is necessary to create the user map and to put onto it  location of control points and their numbers. The user map with put numbers of control points will be used at measurement of control points.

By means of any text editor it is necessary to create a text file of coordinates of control points in CAT format (further a file of source support).

As control points it is necessary to choose long-term contours, i.e. a points, which coordinates are subject to the minimal measurements (for example, crossings of highways, corners of the fundamental constructions, seen points of a geodetic network, etc. and on the contrary, corners of kitchen gardens, border of a wood, etc. are most undesirable). At a choice of points to avoid points, which can appear in a shadow and by that will be badly identified on a photo. At taking of the coordinates of crossing of roads to take the middle of road.

The points selected for survey should be precise and are unequivocally identified on a source raster. To choose 15-25 points on a photo located in regular intervals on all field of a photo.

At work with several photos to provide presence of points, common between photos, i.e. binding points.  

At a choice of points such as crossing roads the points with a corner of crossing, maximal near to a right angle are preferable.

At a choice of points it is necessary to have in view of, that the best accuracy of transformation of a photo is provided inside the area limited to a line, taking place by extremest points, therefore it is necessary to provide a photo with points taking place maximal close to its edges.