Viewing Transformation is the mapping of coordinates of points and lines that form the picture into appropriate coordinates on the display device. Mapping the window onto a subregion of the display device called the viewport is called the Viewing Transformation.
The viewing transformation which maps picture co-ordinates in the WCS to display co-ordinates in PDCS is performed by the following transformations. Converting world co-ordinates to viewing co-ordinates. Normalizing viewing co-ordinates. Converting normalized viewing co-ordinates to device co-ordinates.