Transformation of image features when performing the operations of coordinate transformation has its peculiarities.
Image features can participate in operations of coordinate transformation together with features of other types. Actually only coordinates of raster control points binding undergo transformation. Position of all raster pixels as well as coordinates of raster boundary vertices are calculated automatically basing on control point binding.
In nonlinear coordinate transformations the situation is a little bit different. As it should be expected, coordinates of control points of an image feature are transformed according to the specified nonlinear transformation rule. However, nonlinear coordinate transformation of pixels (points) of raster graphics does not occur. Actually, only displaying of the same raster happens as it was earlier but taking into account new coordinates of control points and boundary vertices.
Shift of features of other spatial types with respect to raster graphics used as a background, as well as shift of image feature boundaries with respect to raster, may be negative results of transformation of this type. Such shifts can occur in nonlinear map transformation since, as it was said before, this operation is performed differently for raster pixels than for map features.
In ObjectLand there is a possibility to perform a special operation of raster transformation. This operation is performed independently of map transformation and the result of this operation will be changing the raster itself, that is, changing the rectangle array of pixels on the basis of which an image feature is built. During map browsing the result of the transformation looks like a shift of raster graphics with respect to the image feature boundary, the boundary itself does not change its position on the map.
To perform raster transformation the corresponding image feature should be selected and the menu command Feature+Edit performed. It is necessary to select the tab “Transformation” in the opened window “Editing image feature” (figure 20-11) and turn on the mode of editing transformation points (the button 
). This mode is available only in the case if binding of feature control points is specified. Besides, the modes of editing control points and feature boundaries should be turned off.
Figure 20-11. Setting image feature transformation
Transformation points are displayed in the pane similarly to control points but they have a smaller size. For adding a transformation point the cursor should be placed in the necessary point and the context menu command Add transformation point performed. The set point can be dragged to another position while holding down the left mouse button. In the pane of list of points source coordinates of the point in the map coordinate system are displayed. They are calculated taking into account control point binding.
A double click on the transformation point or on the corresponding list row opens a dialog box “Target coordinates of point” (figure 20-12). In the fields of this dialog box the user specifies new coordinate values which the point should take after the transformation is performed.
Figure 20-12. Dialog box “Target coordinates of point”
Before the target coordinates are specified, the transformation point is displayed by a red color, and after that it takes light-green color.
The types of possible raster transformations coincide with the types of map coordinate transformations presented in the subsection “Coordinate transformation types”. The number of points required depends on the selected type.
After the transformation type is selected and the transformation points are specified the user pushes the button Perform starting the operation of raster transformation.
If the user is not satisfied with the transformation result, he can cancel the transformation pushing the button Rollback.
The system is able to roll back only one operation of raster transformation. If the user performed several transformations in one window of image feature editing, it will be possible to cancel all of them only when using the button Cancel which stops editing of the image feature without saving changes.
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