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..::tyre tracks in mud::..

Enlarge Screenshot Open up the mud_tracks_start.max file included in the resource zip file. To generate the tracks in the mud we are going to use a particle system to place particles on the surface where the wheel intersects with the ground. These particles will be rendered off to generate an animation which will be re-loaded back into max to displace the plane.
Enlarge Screenshot First we will create the particles that adhere to the tyre and spawn new particles when they hit the ground. Create a Particle Flow system in the Top Viewport. Open Particle Flow and remove the Display, Speed, Shape and Rotation operators. Replace the Position Icon operator with a Position Object operator and add the Tyre object to it. Enable Lock On Emitter and set the Location to Selected Faces. Set the Birth Amount to 20000 and the Emit Stop to 0.
Enlarge Screenshot Add a Collision Spawn test to the event and add the scene’s provided Deflector to it. Set the Inherited Speed to 0 to make the particles static, enable Spawn On Each Collision and set the amount to 100. Create a new event with a Shape Facing operator, wire the new event to the output of the Collision Spawn test and set the Size to 4 to fill in any gaps.Without a rotation the facing particles will face upwards.
Enlarge Screenshot Assign a self-illuminated white material to the event by adding a Material Static operator and instancing the material to the operator’s material slot, size up the plane to the safe frame in the Top Viewport, hide the plane and the tyre and render off the animation with the dimensions of the plane so the resulting map fits perfectly when re-assigned.
Enlarge Screenshot Once the animation has rendered, load the animation back into max as a bitmap map in the Bump slot in the Plane material. Set the Blur Offset to 0.001 to remove any artefacts that may occur when the bump map is rendered, and set the Bump amount to -30 so the white rendered particles depress the surface.
Enlarge Screenshot Finally, we can turn off the particle system, unhide the tyre object and render off the animation. Although this is a material shading effect to give the impression of texture, the result is quite convincing for a shallow depression. Putting all of this knowledge onto a higher detailed wheel we can get some really cool effects with very little effort indeed. This method is suitable for creating slight indentations that have the depth of the tread, but for deeper treads you would have to mix the resulting track animated map with additional maps to control the displacement else we will just get a very high displacement of a tread imprint and not the trench dug out by the tyre. If you want a greater impression in the ground, try using material displacement or a Displace modifier to physically depress the surface, which is used in the final illustration here.
Download the max file! Zip file to accompany.

..::quick tip::..

Try using a Displace modifier instead of bump mapping, or if you’ve got a decent machine try using material displacement!

Initially published: 3D World magazine, Issue 63, April 2005.

Copyright Pete Draper, April 2005. Reproduction without permission prohibited.