Transformation with use of vector map

 Print Previous page Top page Next page

The classical transformation technology of photos supposes use for editorial works of analog photos on the hard carrier. The control points identified on a topographical map are marked onto such photos. In this case for measurement the control points, marked on an analog photo, are used. At measurement of points it is necessary to compare constantly on an analog photo (with help of a magnifier) and on a raster copy of a photo the fragments of the image in a neighbourhood of a measured point.At measurement of points you must  constantly compare the fragments of the image in a neighbourhood of a measured point on an analog photo (with help of a magnifier) and on a raster copy of a photo. All this essentially slows down process of measurement of points. At presence of a vector map it is necessary to use the following technology of building of digital photoplans:

1. Create works region, having included into it available vector maps.

2. Add into  works region a source raster copy of a photo (further a raster).

3. Create user map onto region.

4. Choose two points on a map and to identify points corresponding to them on a raster. It is desirable (but it is not obligatory) to choose points as much as possible distant from each other and on a diagonal of a photo. With help of the Map Editor to put these points on the user map by anyone marked symbol (for example, astronomical points). To put the number of a point near as the label on the user map.

5. Execute transformation of the source raster by two points with scaling. The resulting raster will be approximately overlapped with a vector map. After such overlapping the process of identification of points will essentially be simplified because of narrowing of search area.

6. Close the source not overlapped raster.

7. Choose necessary number of control points on a map for final transformation. To display the chosen points on the user map as well as in 4 item. As a result the point's coordinates on the user map will coincide with coordinates of the corresponding chosen contours of a vector map.

8. Prepare a file of control points (.CAT extension). Coordinates of control points are chosen from a vector map in rectangular system of coordinates.

9. Execute final transformation by EEO in local rectangular coordinates system. As a source raster you must choose a raster, overlapped with a vector map by two points. Choice of actual coordinates you can carry out in Visually by map mode. As control points are denoted on the user map it will be easy to choose them on a raster. The resulting raster will be the final transformed raster.