Dialog Box: Perspective [ Input2 Menu]
If perspective is not in effect, or turned off, the drawing is simply a perpendicular projection down the observer x axis. If perspective is on, the drawing is projected from a point (x,0,0), where x is the perspective distance, onto the plane (0,y,z), that is a horizontal plane passing through the crystal center. Scaling applies to this plane, but obviously fixed scaling has limited intrinsic meaning in perspective drawing; generally the scaling mode Each View Maximum (set in the Scaling dialog in the Input2 menu) should be used when perspective is in effect.
The perspective distance is the distance x of the projection point from the projection plane, or in other words the distance from which the crystal is viewed (distance from the center of the crystal to the eye). Smaller distances will accentuate the "perspective"; larger distances will cause the plot to appear more like a straight-on projection. The perspective distance should be considerably larger than the distance of the furthest corner from the center (or the plane x=0) in the positive x direction.