Adding Rivets: Splines or Decals?

When it came to adding rivet heads to the flat car I had a choice; modelling or bump maps. I decided to test which riveting technique was better.

As a test surface I built a plain cube 12" on a side and added four 1" rivets to the three visible sides. The bare cube.mdl was 1800 bytes.

First I built the lowest cp rivet model I could; 5 cps - four, three sided patches with the bias at the ends of the radial splines cranked up. They're not super smooth (see image at bottom of page) but viewed at arms length they'll do. The single rivet.mdl file was 1524 bytes. Adding twelve to the plain cube produced a model with 54 patches. The model had two groups, cube and rivets. Total model size 8300 bytes.

Then I built a hi-res rivet and added a black to white gradient material to it so a render produces an image where grey scale is proportional to height. I took this rendered image and resized it so a 256 bit pcx file was about the same size as the file for just the lo-res rivet model. No logical reason for this criteria, it just seemed fair. The final bump map was 27 x 27 x 256 = 1567 bytes. Then I applied twelve stamps of this map as a 200% bump in the same locations on the bare cube. The model had one group, cube. Total model size 8252 bytes.

So far, from a storage point of view, its a dead heat. Then I rendered the same 640 X 480 view of each cube. The outputs are shown below. Rendering the modeled cube was 25% faster than rendering the decaled cube. I know which one I prefer but you can interpret these results as you see fit.

rvt_bmp rvt_mdl connectors

And since were on the topic of connectors, the image on the right is a render of connector_hardware.mdl. There's a rivet head, simple carriage bolt head, a hex bolt head, washer and nut (all connected for easy selection), a slotted screw head, a threaded rod and a nut and bolt end. They use as few patches as I think are reasonable. If you're interested in any of these models, send me an e-mail and I'll be happy to send them all in a zip file.

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