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Glossary of Terms

Animation Terms:

  • Keyframing:

    Keyframing is a simple animation technique whereby frames are scripted from start to finish, each frame showing a different location, or orientation, for the object in motion. The software automatically interpolates the frames in between these keyframes. The required keyframe locations are determined first, and then the scripting fixes the length of the animation by setting the number of frames in between each keyframe.



  • Motion Along Paths:

    Curves or lines are defined as paths along which an object, such as a camera, moves. A walk-through might have two paths: one for the camera to follow and one for the target to move along. Scripting involves setting the frame number for the beginning and for the end of each path.



  • Parametric Motion Control:

    Parametric motion control is used in animating complex mechanical parts and assemblies. When an element becomes an actor, the way it moves — position and orientation — is defined as a function of time. For example, the motion of a windmill blade could be defined in terms of revolutions per minute. When scripting this motion time would be expressed in terms of the number of frames (at,say, 24 or 30 frames per second). In an animation of a complex assembly each moving part would be assigned an equation describing its motion.

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Bump Maps:

A texture map or bump map gives a surface a certain tactile appearance: roughness or smoothness, new or, old and beat-up. Typically, this effect is accomplished using grayscale image maps — 256 shades of gray — where white represents the maximum height and black the greatest depth(roughness). MicroStation software is capable of determining the height range and scale of the bump map.

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Raytracing:

Raytracing is a technique for rendering computer images which calculates lines (rays) of light from the viewer's eye point to the nearest surfaces, and then from those surfaces to active light sources, and to other surfaces if a surface is reflective or transparent. Raytracing, therefore, is an especially realistic rendering technique where the surfaces are reflective or transparent, such as metals, water, mirrors and glass. The raytracing calculation is view-dependent since only the lines of light visible from the viewer's position are calculated. Each time a different camera angle or position is chosen, an entirely new raytracing must be calculated. Most of the illumination calculated is direct light: from the light source to the surface. The only indirect light calculated comes from rays received by reflective surfaces, or from rays refracted through transparent surfaces. For interior models where the dominant material finish is matte (the received light scatters) rather than glossy (the received light reflects), light sources must be supplemented by ambient (nonattributable) light to create the appearance of soft, realistic shadows. For raytracing high resolution images of complex models, extensive RAM and a fast processor is necessary. All of the images on this website have been raytraced.

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Radiosity:

Radiosity solving is a rendering technique which calculates all the light which is emitted from diffuse (light scattering) surfaces. It is a view-independent solution in that once all of the design objects and active light sources are in place, the resulting radiosity solution can be applied to any view or animated walk-through of the design space. Raytracing (see above) and radiosity are used in combination: the radiosity calculation first accounts for all of the indirect illumination, then the raytracer, using the radiosity solution, calculates highlights and reflections specific to each chosen view. Since a light ray can reflect off of many diffuse surfaces — each successive reflection generating a lower light value — radiosity solving is an iterative process. The user can specify at the outset how much light power is shot (the number of iterations) before the process is terminated. Radiosity's unique benefits include: soft shadows with subtle transitions, and color tinting of one surface by reflected light from a nearby colored surface. Radiosity solving is much more complex, and compute-intensive, than the raytrace technique used alone; but it yields results, in some cases, which are well worth the extra effort. Good candidates for radiosity are less complex interior models with a predominance of matte-finish materials, such as light painted surfaces. As computer speeds approach and go beyond 1GHz, and as radiosity solvers become more sophisticated, their popularity is rising.

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