Glossary - An Introduction to Computer Graphics for Artists - page 305

Parameter A variable that defi nes a specifi c value within a fi xed formula.
Parent Node The top node of a hierarchy .
Periodic Curve A curve without beginning or end. To defi ne a periodic curve, the
endpoints must cross with at least two overlapping CVs on either side of the join,
for a total of fi ve CVs. These must all have the same tangent. If these conditions
are satisfi ed, and the curve is identifi ed to your software as “periodic,” then it
will be periodic.
Perpendicular Meeting at a 90° angle with a given location.
Perspective A system used for projecting a three-dimensional scene onto a two-
dimensional surface .
Photon A virtual light unit consisting of various properties in common with a ray
but with the added property that it can continue bouncing until all of its light
energy is expended, causing a more accurate lighting simulation than raytracing.
Pivot A coordinate around which a translation operation may take place.
Pixel The smallest visible unit used in computer-based raster graphics .
Planar A condition where all points in question lie within the same plane.
Planar Projection To project texture coordinates based on the normal direction of
a single plane.
Plane A fl at surface of determinate extent.
Point A dimensionless object with no properties other than location. In CG, fl ags
and other properties may be attached to a point without changing the character of
the point.
Pointillism A style of painting popularized by the work of Georges Seurat,
inspired by the work of the Impressionist painters, including that of Claude
Monet and Pierre Auguste Dominique Renoir.
Point Light A light source that casts light in all directions from its location.
Poly Budget The number of triangles, or polygons, allocated for a given use.
Polycount The number of triangles or polygons contained in a given polyset.
Polygon A geometric primitive containing a minimum of three vertices, three
edges, and a face. It can have only one face, but any number of vertices and edges
above the minimum.
Polyset A group of polygons, whether or not they are topologically contiguous,
that are treated as a single object-level entity.
Pre-rendered Graphics Used to defi ne the difference between using a sequence
of image fi les as an end product from 3D objects that are rendered directly to
screen, or real-time graphics .
Primitive A polyset defi ned by a parametric formula.
Production Design A trade specialty of designing the look or style of a given pro-
duction. Production designers are most often employed in fi lm, television, and
theatre, but are increasingly working in the video game industry as well.
Proportionate Similar to aspect ratio , the relative measure of related objects, or
internal ratio of different dimensions within the same object.
Project To push forward, usually in a perfectly straight line, either along a constant
axis or a variety of normals, for the purpose of calculating intersections with
geometric objects or elements.