Transformation by elements of external orientation

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Transformation by elements of external orientation (EEO) is used for transformation of photos when parameters of photographing are known. It consists that by a set of source control points (their theoretical and actual coordinates in one system of coordinates (CS)) EEO will be calculated, with help of which then the transformed raster oriented on district will be received.

For transformation by EEO the following source data are necessary:

- Theoretical coordinates of control points (not less than five points).

- Type of a photo.

- Focus of a photo.

- Admission.

- Height of photographing.

- Coordinates of the main point.

- Central label (cross).

- Distortion of objective.

- Displacement.

 

Type of a processed photo is defined by a design of the camera. The user before construction of the photoplan with use of EEO is obliged to find out: by what type of the camera a photo is made, and what focus of this camera? At absence of the exact data on focus it is possible to be guided by the following:

- focus of an aerial photo is about        100 mm;

- focus of a panoramic photo is about 1000 mm;

- focus of the central photo is about    3000 mm;

- focus of a slot photo is about           2200 mm or 3000 mm.

 

Optional parameters or are absent in general on a photo (for example the central cross), or they not were found out. Use of optional parameters leads to increase of accuracy of a created orthophotomap, therefore at their presence it is recommended to use them.

If the type of a photo precisely is not known, then it is possible to try to process a photo in a mode of the central photo, though thus losses in accuracy of construction of the photoplan are possible.

If onto the works region there is a matrix of heights it can be used in calculations of elements of external orientation. Otherwise,   average by a support height will be used.

Information necessary for transformation of a photo is kept in a text file of transformation parameters, which is created at closing the task, and can be used at the following starting of the task.

Theoretical coordinates of control points are taken from the catalog of theoretical coordinates. Control points should be no more than 500.

You can receive actual coordinates of control points, having specified actual position of points on a raster. Thus a text file of the catalog of actual coordinates and user map with control points will be automatically created. Besides, numbers of the specified points are saved in a file of parameters.

To choose control points it is necessary to press Select points button (Choice of control points).

For a turn of a photo and finding of position of the beginning of coordinates in system of a photo it is necessary to specify labels. To specify their position on a raster, it is necessary to press Measure labels button.

To specify position of control points on a raster, it is necessary to press Measure points button (Measurement of control points.).

By OK button the process of transformation is started. The information about expected accuracy of the received raster image is displayed on the screen, thus on the basis of precomputation it is possible to solve, whether to transform a raster by the given set of control points or to try other variant.