Fundamental Problems in Geometry - Cont.
The objects represented in the modeling coordinates are first placed into appropriate positions within the scene using a reference frame called world coordinates. Then the world coordinate description of the scene is transformed to one or more output device reference frames for display. These display coordinates are referred to as device coordinates or screen coordinates, in case of video monitor. Generally, in a graphic system the world coordinate positions are first converted into normalized device coordinates, in the range from 0 to 1 before final conversion to specific device coordinates. This conversion makes the system independent of the various devices that might be used at particular workstation, e.g.
If we attribute to the monitor screen, planar(s, t) coordinates with s horizontal and t vertical, measured in length units (mm or inches) from the origin at the bottom left corner of the screen. This we call screen coordinates. Let b be the width and h be the height of the display area. So s and t can range from 0 to b and from 0 to h respectively.
u = s/b
v = t/h
These ratios (u, v) are referred to as Normalized Screen Coordinates, measured also with reference to the conventional origin at the bottom left corner O of the display area. The maximum values that can be taken by s and t are b and h respectively, u and v can only range from 0 to 1.