There are two transformations that operate between the model space and the page space:
All three model transformation types and the viewing transformations can be considered a part of the picture. The default viewing transformation is part of the environment, and must not be used for picture construction.
Viewing transformations only apply in retained or nonretained segments. The viewing transformation attribute is set to the presentation space viewing transformation matrix value at the start of each drawn root segment and remains constant for that segment. If GpiSetViewingTransformMatrix is called, the new value is not used until the next segment is opened. The matrix drawing attribute is reset to identity at the end of the segment. Each change in a viewing transformation is equivalent to defining a new model space.
The default viewing transformation is a presentation space attribute and should not normally be modified in the middle of a picture. This attribute can be updated by GpiSetDefaultViewMatrix.
A picture is normally constructed in the presentation page with an identity default viewing transformation. The default viewing transformation can then be used to scale and scroll the entire picture in the presentation page.