REDEFINE TRANSFORMATION

Purpose:

This function is used to display and possibly redefine the transformation history of user-indicated subpictures. The transformation history is used by the system to map between world and drawing coordinates. This is necessary to maintain consistency within the drawing, such as for example

• exchanging subpictures

• saving or inserting subpictures

• retrieving the scale of subpictures

The transformation history is automatically maintained by the system and is normally no subject for user redefinition. There are, however, circumstances in which such a redefinition is justified, namely when the user wants to control the neutral format of subpictures saved in the data bank. See help about Insert Subpicture for a discussion of this neutral format.

Instructions:

1. In the Tools menu, click Subpicture, then Redefine Transformation.

2. Viewing the History

   The subpicture of interest is indicated by user. Once indicated, a multiple choice dialog presenting the transformation history will appear. The history includes the following attributes:

   • Reflection
     (None/U-axis/V-axis)

   • Rotation angle
     (in degrees)

   • Scale
     (absolute)

     It should be mentioned that the translation also is a part of the history. Because this attribute should be of no interest for the user, it is hidden and hence cannot be redefined explicitly by user.

     It should be mentioned that the translation also is a part of the history. Because this attribute should be of no interest for the user, it is hidden and hence cannot be redefined explicitly by user.

     When ready, click Cancel to view another history, or Quit to leave this function.

     To redefine the history, select the appropriate attribute for update.

3. Redefining the History

To redefine the reflection, select the Reflection alternative. A new dialog showing the possible alternatives will appear:

• None

• U-axis

• V-axis

  Select between None, U-axis and V-axis.

  To redefine the rotation, select the Rotation alternative. The desired angle, in degrees, is then keyed in by user (the current value is proposed by the system).

  To redefine the scale, select the Scaling alternative. The desired scale factor is then keyed in by user. A scale factor given as a single value (that means, not containing ':' or '/') is always interpreted reciprocally (both 50 and 1:50 means 0.02).

  The redefinition will be applied on the subpicture instantly and the resulting transformation history will be presented to the user.

Example of Justified Use

As mentioned above, the use of this function could be justified as a necessary step prior to saving of a subpicture on the data bank. Now, imagine that the user wants to fetch a subpicture in the data bank, modify it somewhat and finally save it back in the data bank. Lets assume the following steps:

• Fetch the subpicture, using the function Insert Subpicture

• Rotate the subpicture 45 degrees, using the function Transform Subpicture. When applied, the transformation history of the subpicture will be updated with this rotation.

• Save it back in the data bank, using the function Save Subpicture

The result of the save operation is nothing! This is because the 45 degree rotation, applied on the subpicture, was automatically added to the transformation history as well. When saving it back in the data bank, the inverse of the transformation history was applied on the subpicture to make it saved in neutral format. The user modification was lost!

To force the system to include the user modification in the data bank, you have to make the system forget this modification before storing the subpicture. This is done by redefining the transformation history of the subpicture. Just decrease the rotation angle of the subpicture with 45 degrees before storing it in the data bank.

Options:

None.

Result:

The transformation history is displayed and possibly updated by the user.