Full Stream Ahead.(Technology Information)

A new technology delivers large 3D models across the Web

Big models and real-time interaction can spell big trouble for the Web, but they can also spell big success for applications relying on consistent, high-quality 3D content delivery--from e-commerce to collaborative engineering to entertainment. Such applications rely on the fast transmission of visually realistic 3D objects to capture and keep the interest and excitement of end users, yet the cost of visual realism is large datasets. The enormous number of polygons needed to represent 3D objects and scenes in a pleasing manner places a tremendous burden on maintenance, storage, and computational resources.

Only recently, with advances in 3D graphics boards, have modelers and animators been able to display high-quality images in real time. Researchers are now scrambling to develop techniques to deliver the same high-quality 3D content over the Internet quickly and reliably. Toward this end, graphics experts at Tel Aviv University have thrown their hats into the ring with the development of a novel 3D streaming technology. The system uses a technique through which polygonal meshes are compressed into a progressive stream (minimizing requisite storage space) and delivered to client computers using asynchronous transmission.

"The key point is that the compressed stream inherently contains levels of detail such that any prefix of the stream represents a coherent approximation of the 3D model," says Daniel Cohen-Or, an associate professor at Tel Aviv University and one of the chief architects of the new streaming technology. "Thus, the end user can view and interact with an approximation of the 3D models up to the optimal level of detail, enabling real-time interaction and a quicker response time."

First Impressions

The system is founded on the premise that the initial view of (and ability to interact with) a 3D object is critical because users are reluctant to wait out long download times. "The image of true interactive 3D models should appear on the end-user screen at least as fast as common still images appear, without compromising the rendering quality," says Daniel Cohen-Or. For this to happen, he notes, "it is crucial to minimize the overall size of the 3D content stream and the rendering time of the first view."

The first component of the streaming technique is a lossless mesh-compression method. A "mesh" refers to the collection of polygons (typically triangles) that form one or more 3D surfaces in space, which together define an object's geometry. In order to compress such data without losing information, both the geometric information and the connectivity information (the relationships among vertices and triangles) must be maintained. The Tel Aviv team achieves this using a hierarchical-decomposition technique in which, in a preprocess, a simplification algorithm is applied to the original triangular mesh to iteratively remove sets of vertices, generating a series ...