perspective [ on | off ] [ dscale= scale]
Turn on perspective projection, which aids in seeing depth.
Turn off perspective projection and use orthographic projection. This kind of projection lacks depth cues.
This allows the user to scale the amount of perspective by changing the distance from the eye to the viewplane. The default is 2.0.
The perspective command toggles between perspective and orthogonal projection, and allows the user to set the amount of perspective. Issuing the command with no options, or with just the dscale option, automatically turns on perspective.