` COMPUTE! ISSUE 153 / JUNE 1993 / PAGE S8`

 3D graphics glossary. (Compute's Getting Started with 3D Graphics) (Glossary) by Steven Anzovin axis. One of the three Cartesian screen directions. The x-axis is along the screen horizontal, the y-axis is along the screen vertical, and the z-axis goes into the screen picture space. 3D objects also have their own axes, a cylinder's axis is its centerline. extrusion. Creating a 3D shape by stretching a 2D shape along a third axis, much like squeezing a plastic block through a shaped nozzle. Used most often to create 3D lettering. fractal geometry. A branch of mathematics that explains how to produce irregular, lifelike landscapes and branching forms with simple formulas. hierarchical object. A 3D object whose motion is linked to the motion of other objects according to levels of influence. in-betweening. Drawing intermediate positions of an animated object between the key frames. The in-between frames are called tweens. See key frame. key frame. In 3D animation, pictures that define the beginning and end of an animated sequence. mapping. The process of adding a texture, pattern, picture, or reflection to the surface of a 3D object. Modeling. Creating 3D objects by modifying primitives or editing the points of polygons or splines. path. The trail along which a 3D object travels in a 3D animation. polygon. A flat geometric shape used to create the surface of 3D objects in some modeling programs. primitive. A s like a cube or sphere, that acts as a starting point for creating 3D objects. ray tracing. Highly realistic method of 3D rendering that traces the path of a ray of light from the eye's point of view to every element in the scene. See rendering. rendering. The realistic imaging of a 3D object or scene by adding colors, shading, textures, transparencies, shadows, and reflections. shading. Simulating the effects of light shining on a 3D object. solid model. A 3D object with simple shading and hidden areas removed. spinning. Creating a 3D object by rotating a 2D shape around a central axis. For example, a sphere can be created by rotating a circle around its diameter. Also called lathing. spline. A curve defined by a mathematical formula. Used by some programs to achieve smoother surfaces for 3D objects than can be obtained by using polygons. Animated 3D objects also can move along spline-based paths. vertex. The corner of a polygon. One of the editable points of a 3D object. wire-frame. A 3D object depicted as a hollow structure of lines. A wire-frame image retains the shape of the object while cutting down on the computation needed to represent it. world. The environment of a 3D object or objects.