Adaptive Level-of-detail in SVG

author: Yi-Hong Chang, Tyng-Ruey Chuang and Hao-Chuan Wang
publication date: September 2004
cite this with: Yi-Hong Chang, Tyng-Ruey Chuang and Hao-Chuan Wang. Adaptive Level-of-detail in SVG. In SVG Open 2004: 3nd Annual Conference on Scalable Vector Graphics. Tokyo, Japan. September 2004.
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copyright: all rights reserved
category: XML and Web Technologies
tag: Adaptive Level-of-Detail, Adaptive zooming, Rich/Smart graphics, SVG
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A script-free SVG document is just data with a fixed internal structure and exhibits only static graphic semantics. If SVG documents are not data but are programs, then one should be able to use SVG to create dynamic graphics, as the documents would be executed for its dynamic semantics. When SVG documents are used with scripting, one can achieve a certain level of dynamic graphics. However, the logics of the dynamic graphics is kept in the script, not expressed in the document itself. This is a drawback, as often one may like to express the graphic semantics entirely within SVG elements. For example, one may want to use only SVG elements to describe graphics that animate, or to express graphics with adaptive Level-of-Detail (LoD). Animation is supported in SVG with a built-in vocabulary, or even by the help of external vocabulary such as SMIL. Currently there is no support of adaptive LoD in SVG, although it is extremely useful in Geographic Information Systems (for adaptive zooming) and fractal geometries (for on-demand resolution-dependent visual presentation).

We show in the paper how to support adaptive LoD in SVG. The SVG DTD is extended by adding attributes to the elements (including visual elements and grouping elements). Information about the adaptation function and the current detail-level can now be kept with the SVG <g> element, which is a focal point to be further explored. When more details are demanded, these attributes are used to generate the next level of details for elements enclosed in the current focal point. The newly produced graphic elements then replace the old ones, and become the new focal points. Currently the adaptation functions are expressed by an ad hoc transformational language, and they are interpreted by an ECMA script. We note that existing XML transformational languages (such as XSLT) and vocabularies (similar to SMIL for animation) can also be used to express adaptation, and they can lead to a script-free but LoD-capable SVG.

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