Terms

Terms

The calibration procedure transforms a raster image in such a way that the given set of image points moves to another set of points with pre-defined coordinates. The number of points and their locations are arbitrary.
The calibrating transformation is defined by the set of calibration pairs and the calibration method used.

Calibration Pairs

To prepare calibration, specify vectors of point movements. This can be done by specifying a set of calibration pairs. Each pair represents two locations of the point its current location on the image (measured point), and its required location (real point).

Calibration Methods

A calibration method is a parametric transformation function used for calibrating. The program offers a number of calibration methods: affine, bilinear, polynomial, surface splines, etc.
With some sets of calibration pairs and some calibration method, the program cannot make a transformation of the given type that where all measured points move to appropriate real points. This produces calibration deviation distances between the points obtained as a result of transformation and their appropriate real points. When choosing a calibration method, use the minimizing of the square error value for all calibration pairs as criteria.

Calibration Pairs types

Every calibration pair has one of the follow types:
*Grid*– if a pair is a part of a calibration Grid, used in calculation of calibration parameters and estimating calibration accuracy.
Control – if a pair is used in calculation of calibration parameters and estimating calibration accuracy.
Check – if a pair is used only for estimating the calibration accuracy and does not affect the calibration parameters.
Unused – if a pair is not used in calculation of calibration parameters and estimating calibration accuracy.

The main steps of Calibration

1. Open the Calibration dialog box.
2. Create a set of calibration pairs.
3. Specify the measured point’s positions.
4. Choose an appropriate calibration method.
5. Run calibration.
Note: it may be useful to define the coordinate system, the coordinate system origin and scale before the calibration
 For more information on defining the coordinate system see Command Line.