2013

periodic curve
A smooth, closed curve such as a circle. Because its control vertices are not
tangent to the object, if the curve is reshaped, it stays smooth and does not
create kinks. See also clamp curve.
periodic surface
A smooth, closed surface such as a cylinder. Because its control vertices are
not tangent to the object, if the surface is reshaped, it stays smooth and does
not create kinks. See also clamp surface.
perspective view
Objects in 3D seen by an observer positioned at the viewpoint looking at the
view center. Objects appear smaller when the distance from the observer (at
the view point) to the view center increases. Although a perspective view
appears realistic, it does not preserve the shapes of objects. Parallel lines
seemingly converge in the view. The program has perspective view settings
for VPORTS table entries as well as viewport objects.
photometric lights
Photometric lights are physically-correct lights. Physically correct lights
attenuate as the square of the distance. Photometry is the science of
measurement of visible light in terms of its perceived brightness.
photon map
A technique to generate the indirect illumination effects of global illumination
used by the renderer. When it calculates indirect illumination, the renderer
traces photons emitted from a light. The photon is traced through the model,
being reflected or transmitted by objects, until it strikes a diffuse surface. When
it strikes a surface, the photon is stored in the photon map.
photorealistic rendering
Rendering that resembles a photograph.
pick button
The button on a pointing device that is used to select objects or specify points
on the screen. For example, on a two-button mouse, it is the left button by
default.
780 | Glossary