3D Animation Workshop: Lesson 83: 3D E-Commerce With MetaStream

Lesson 83 - 3D E-Commerce With MetaStream- Part 3

The heart of the MetaStream technology is the MetaStream file format, developed by MetaCreations and Intel and currently in its 2.0 version. 3D artists with experience in NURBS modeling (a subject addressed some months ago in these columns) understand the concept of variable geometric resolution. A NURBS surface is free-form and ideal. However, to be rendered, its must be resolved into a polygonal mesh, a process called tessellation or surface approximation. The single most important aspect of NURBS modeling is in this very power to vary the geometric resolution of the model as needed. If the model is small or needed for realtime rendering, the tesselation can be made cruder to produce a lower polygon count. For close-ups or cinematic-quality work, the surface approximation can be made very fine.

The games industry, which is the technology leader in realtime, interactive 3D graphics, is moving toward the goal of realtime tessellation of NURBS models. Thus a NURBS character could seamlessly increase its geometric resolution (polygon count) as it grows large on the screen, and decrease it's resolution as it moves away. This technological advance, when it occurs, will dramatically increase the quality and realism of interactive 3D.

But MetaStream has managed to achieve the similar results with straight polygonal meshes. The essence of the MetaStream file format is information that permits the viewer plug-in to change the geometric resolution of the object, by following a Vertex History. Additional vertices are added to the mesh to increase resolution or subtracted from it to decrease it. This remarkable power can serve two purposes. First, it can be used to support streaming so that a low-poly version of the model loads first and the resolution builds over time. Thus the user sees at least something rather quickly, and users with slow connections are less likely to bail out during download.

Second, once the model is fully downloaded, the resolution can be adjusted to suit the power of the local processor. For example, assume that the developer wants to ensure a frame rate of at least 10 frames per second (10 fps) to provide a smooth animated effect when rotating the model. If variable resolution is used, the model will be automatically simplified by eliminating vertices until the polygon count is low enough to render at the desired frame rate. This is the key technological advance in MetaStreams and the strongest argument for its future.

You've got to check this out for yourself. Once the plug-in is installed, take a look at an object on one of the Sony sites. Zoom in as much as you want and notice that the geometry is quite smooth. This is because you're looking at the highest resolution version of the model. Right-click in the window and note the range of viewer options that appear on a menu. Change from a smooth shaded view to a wireframe view. Now you can actually see the polygonal mesh. Rotate around to understand the model.

By default the variable resolution option is off, so turn on the Auto-Resolution option in the right-click menu. Start rotating and see what happens to the mesh. If you have a powerful system, it may be that nothing will change because you're getting the minimum desired frame rate. But I tried it on a very slow old system and the model immediately collapsed to a low-poly version. It was far too crude for my taste, but it did rotate easily, and it proved that this key aspect of the technology works.

We'll look deeper into MetaStream next time, but those who are interested in the rapidly evolving state of 3D for the Internet will benefit from a visit to the MetaCreations and the MetaStream Web sites.

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Created: Jan. 5, 2000
Revised: Jan. 5, 2000

URL: https://webreference.com/3d/lesson83/part3.html