One Optimization of an Earlier Model of Virtual Downtown Ann Arbor
Klaus-Peter Beier*
The University of Michigan
     In Ann Arbor, Michigan: Virtual Downtown Experiments, Part III, Solstice, Vol. XIII, No. 2,  the authors, Kwon, Lazzaro, Oppenheim, and Rosenblum, portray a useful virtual model of four blocks of downtown Ann Arbor.  The file size of their model is, however, quite large:  40 MB.  This article iillustrates one way to reduce the size of that file and, consequently, load time.  The newly optimized file is now 8 MB which is useful to a wider audience than is the previous file.    The appearance of the two files does not differ greatly; what does differ is load time. Figure 1 below shows a screen capture from the 40 MB file set at High resolution; Figure 2 below shows a screen capture from the 8 MB file set at Medium resolution and modified as noted below.  The optimization for improved load time does not make a noticeable difference in visual appearance.  Figure 3 shows the edited 8 MB vrml file embedded in the html (requires that Cosmo Player or Cortona be pre-loaded in the browser; both are free downloads).
 

Figure 1.  Screen capture from the 40 MB file set at a viewpoint, zoomed in on, and lightened in Adobe Photoshop (trademark, Adobe). Link to VR file:  requires Cosmo Player plug in to browser (IE or Netscape 4.x) or Cortona from Parallel Graphics (free download).

Figure 2.  Screen capture from the 8 MB file set at a viewpoint, zoomed in on, and lightened in Adobe Photoshop (trademark Adobe). Link to VR file:  requires Cosmo Player plug in to browser (IE or Netscape 4.x) or Cortona from Parallel Graphics.  This linked file is also shown embedded in the html, below.

Figure 3.  Edited file.  Try looking at the model from different viewpoints or navigate, on your own, using the control panel.

Still, the application is big and runs slowly (low frame rate) if the most advanced graphics board is not available. The culprit is the artifacts file. The artifacts (trees, lamps, benches) are over-defined (too many polygons).  Also, exhaustive field checking is a recommended future step to remove any error in detail in the scene as compared to reality.  The appendix to this document, made from notes, shows the modifications made to the files.
 

APPENDIX

Removed option for low-res and high-res textures, using only med-res textures.
This eliminates all jpg files for high and low res.

Changed all file types to lower case (e.g. WRL -> wrl)

Removed all instances of Lamp (43 lamps) from artifacts.wrl
Created Inline file for lamp: LAMPUS.wrl
Created prototype MyLamp using Inline file
This reduced the size of artifacts.wrl

Same for 46 trees

Same for 7 benches

Removed all TimeSensors connected to trees (no need)

Modified many instances of "solid FALSE" to "solid TRUE"

Removed invalid color in Lamp

Removed reference to non-existing texture REKKANIG.BMP

Cleaned up ROUTING and Script

Set "collision FALSE" for all artifact.wrl objects

Improved navigation, added useful viewpoints

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Professor Beier, Ph.D., is Director of the 3D Laboratory of The University of Michigan Media Union
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Solstice:  An Electronic Journal of Geography and Mathematics, Institute of Mathematical Geography, Ann Arbor, Michigan.
Volume XV, Number 1.
http://www.InstituteOfMathematicalGeography.org/