4.3.9. Transformation
With the function Calculate
> System Transformation the surveyed points or coordinates can
be transformed from one coordinate system into another existing system (see Initial
> System) via identical points. After clicking the menu item, a
dialog box appears in which the destination system is selected.
After selection of the destination system, the points in the source system are
displayed.
By
clicking the button <Ctrl Pnts>, the
existing control points (identical points in both systems) automatically
identified by GART-2000®
CE can
be displayed. With <Enter> or <Delete>
the list of control points can be modified.
Depending
on the selected type of transformation, two or three control points are
required. If an insufficient number of control points is available to calculate
the transformation parameters, a corresponding error message pops up in GART-2000®
CE.
The
transformation type can be fixed by clicking the button <Transf.>.
The 4-Parameter Transformation is used in GART-2000®
CE as standard. However, the following transformation types are also
available:
- 3-Parameter
Transformation: the scale factor m is set to 1, calculations comprise the
displacements in the x- and y-direction as well as the angle of rotation j of
the coordinate system.
-4-Parameter Transformation: the scale factor m is calculated in addition to the
3-Parameter Transformation.
- 5-Parameter Transformation: in contrast to the 4-Parameter-Transformation, a
uniform scale factor m is not determined, but rather the respective scale
factors mx and my for each coordinate axis.
- 6-Parameter Transformation: in contrast to the 5-Parameter Transformation, not
only a rotational angle is calculated, but also a separate angle of rotation for
each coordinate axis (shearing, the rectangularity is abandoned).
The
respective transformations can be calculated with or without residual
estimation. In the residual estimation, a coordinate adjustment with
neighborhood in-fitting takes place, i.e. the control points are mapped onto
themselves. The elevations of the points in the destination system are
calculated from the mean height difference of the control points. After
the transformation parameters have been calculated, these are displayed in a
dialog box.
If an adequate number of control points have been specified in the control point
dialog, this can be quitted via the <X>
button. The user is returned to the transformation dialog. After pressing
the button <Calculate.>, the
transformation is performed as soon as the point range to be transformed is
specified.
The transformation dialog is quitted with <X>.
The transformed coordinates can be examined via the menu Output > Coordinates
after a change of current system (Initial
> System).