Graphics Viewports have coordinate systems with the origin at the centre
of the screen. Depending on the aspect ratio of the device, the longer of the
X or Y Axes will span the range (-1.0,+1.0), the other axis spanning (-R,+R)
where R is the normalised aspect ratio (lies in the range 0.0 to 1.0). The
dimensions of the Viewport that completely fills the screen may be determined
by the Application Programmer through the use of a UIPACK Subprogram.
UIPACK uses the DI-3000 Graphics Package for its low level graphics so the
conventions for Viewports and Windows are described in the documentation for
that package. The CDF MENU Package (CDF-236) is used by UIPACK in order to
manage Graphics Viewports and any of the Subprograms provided by that Package
are available for use by the UIPACK Programmer.