When graphical objects are composed into a picture, it is necessary to have a mapping between the coordinate system of the graphical object and the coordinate system of the picture, since each graphical object is defined in its own coordinate system and is placed somewhere in the coordinate system of the picture.
The graphical object defines a transformation from its own coordinate system to the coordinate system of the picture. Since the coordinate system of the shape is identical to the coordinate system of the graphical object it is part of, the transformation actually defines how to position the shape of the graphical object in the picture. This transformation is described in a matrix called TM, inherited from the superpattern AbstractGraphicalObject.
See also the description of the Transform attribute of graphical objects above (Transforming Graphical Objects).
The Bifrost Graphics System  Reference Manual  © 19912004 Mjølner Informatics 
[Modified: Monday October 16^{th} 2000 at 13:43]
