Smooth Levels of Detail

Incremental Encoding of Polygonal Models
Project duration: 1996-1997
Contact: Dieter Schmalstieg, Gernot Schaufler


A new representation for geometric objects allows incremental refinement of the visual fidelity as data is sent over a network, and also yields significant compression.


Every application that needs to send geometry data over a network benefits from the approach, such as distributed virtual environments, concurrent engeneering, and collaborative visualization.


Geometric representations of objects must usually be available completely before the data is usable, so users always have to wait for downloads to complete.


"Smooth LODs" are a method to generate a stream of data which continuously refines a polygonal model from the coarsest representation to the original high-fidelity model. Unlike conventional level of detail algorithms that use only a small number of discrete approximations for each object, our method allows a smooth, continuous refinement of the object over time while the stream is transmitted.

The approach is based on a hierarchical clustering algorithm which produces the model representation of steadily increasing detail and has several advantages over conventional models with few, discrete levels of detail: The model can be transmitted and decoded incrementally, yielding a valid approximation at any stage of the process. The incremental encoding is extremely compact, so models are smaller than in their original form. Any desired level of detail can be selected during rendering at interactive speed. It is also possible to have variable detail resolution within a single model, which is useful for rendering models with large extent.


Smooth Levels of Detail : D. Schmalstieg, G. Schaufler

DOWNLOAD Download SGI (IRIX) demo executable of Smoothlods (ZIP file, 1MB)

COMPARISON The image to the left is a omparison of 3 development stages of an object. The left column shows smooth LODs, the right column conventional LODs for corresponding amounts of data. Black bars on each side indicate the amount of triangles received and displayed.

Download QuickTime movies that visually compare smooth LODs and conventional LODs side by side. On the left side of each movie is the smooth LOD, on the right side the conventional LOD. The red bar on the left and the blue bar on the right grow as more triangles become available for each algorithm.

Movies with zoom (showing how you would use the smooth LODs in a real application):


Movies without zoom (demonstrate how smooth LODs work at a close-up):

Lamp (without zoom)
Ball (without zoom)

This page is maintained by Dieter Schmalstieg. It was last updated on October 29, 1997.
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