5 Calibrating Raster Images
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To create calibration pairs:
1.
Specify the known theoretical point coordinates (
real points
). There are two
ways to do this – define a calibration grid or add them one by one. Both
methods may be used simultaneously. Upon creation, each calibration pair
has the same measured and real point coordinates.
2.
Specify the appropriate measured points for all real points by picking them on
the image or entering the point coordinates from the keyboard.
Defining Calibration Grid
A calibration grid is helpful when calibrating images covered with the raster grid with
nodes that must have known coordinates. Such images are, for example, scanned
images of maps or geodetic plans.
Defining a calibration grid creates a set of calibration pairs placed in the nodes of a
rectangular grid. These calibration pairs have the
Grid
type.
The position of grid nodes is determined by the origin, angle, cell size and the
number of cells in the vertical and horizontal directions.
Þ
There can only be one grid defined on the image. Redefining a calibration
grid removes all calibration pairs of the present grid from the image.
To define a calibration grid
1.
Open the Calibration dialog box.
2.
Click the
button in the
Calibration
dialog box.
The
Calibration Grid
dialog box appears:
Calibration Grid dialog box
3.
Specify the grid origin.
Enter its coordinates into
Origin
, or press the
Measure
button and click the
origin location on the image.
The grid origin is assumed to be in the lower-left corner, and the grid is
generated along the positive direction of the X and Y axis. To set a different
corner and grid direction, set negative values in
Size
and
Cell
boxes.
4.
Specify
X Size
and
Y Size
of the grid cell.