From: jimh@surreal.asd.sgi.com (Jim Helman)
Subject: Re: MISC: VR Slang request
Date: Fri, 26 Mar 1993 18:14:57 GMT
Organization: Home for Degenerate Physicists



Here are a few terms borrowed from the rendering and visual simulation
worlds.

Aliasing.  An undesirable visual artifact of many 3D renderings.
Creates jaggies along the sides of objects and flickering of objects
smaller than a pixel.

Scintillation.  The "sparkling" of textures or small objects.  Usually
undesirable and caused by aliasing.

Culling.  Removing invisible pieces of geometry and only sending
potentially visible geometry to the graphics subsystem.  Simple
culling involves rejecting objects not in the view frustum.  More
complex systems take into account occlusion of some objects by others,
e.g. a building hiding trees behind it.

LOD (Level of Detail).  A model of a particular resolution among a
series of models of the same object.  Multiple LODs are used to
increase graphics performance by drawing simpler geometry when the
object occupies fewer pixels on the screen.  LOD selection can also be
driven by graphics load, area-of-interest, gaze direction, etc.

Fade LOD.  Blending between two LOD models rather than doing a hard
switch which can cause a visual pop.

Pop.  When an object's visible appearance suddenly changes or an
object appears out of nowhere.  Usually an undesired artifact of poor
LOD.

Detail Texture.  A texture superimposed on another texture to increase
the apparent resolution of the original texture image.  Used when the
eyepoint is so close to the textured object that the base texture is
being magnified (i.e. one texel in the texture image being mapped to
many pixels on the screen).  A detail texture, typically a noise
image, is blended into the image at a higher resolution adding a
gritty realism to the appearance of the object.

Texture Swimming.  Unnatural motion of static textures on the surfaces
objects as they are rotated.  Caused by quick and dirty texture
interpolation in screen coordinates.  Correctable by subdividing
polygons sufficiently or by doing perspective correction.

rgds,

-jim helman

jimh@surreal.asd.sgi.com
415/390-1151