The ViewCube tool supports two view projection modes (Perspective and Orthographic)
and a combination of both these modes (Perspective with Ortho faces). Orthographic
projection is also referred to as parallel projection. Perspective projected views
are calculated based on the distance from a theoretical camera and target point. The
shorter the distance between the camera and the target point, the more distorted the
perspective effect appears; greater distances produce less distorted affects on the
model. Orthographic projected views display all the points of a model being projected
parallel to the screen.

Orthographic projection mode makes it easier to work with a model due to all the edges
of the model appearing as the same size, regardless of the distance from the camera.
Orthographic projection mode though, is not how you commonly see objects in the real
world. Objects in the real world are seen in perspective projection. So when you want
to generate a rendering or hidden line view of a model, using perspective projection
will give the model a more realistic look.

The following illustration shows the same model viewed from the same viewing direction,
but with different view projections.

Parallel

Perspective

When you change the view for a model, the view is updated using the previous projection
mode unless the current projection mode for the ViewCube tool is Perspective with
Ortho Faces. The Perspective with Ortho Faces mode forces all views to be displayed
in perspective projection unless the model is being viewed from one of the face views:
top, bottom, front, back, left, or right.