Welcome to another Home Run Pictures "Inside the Production" page. This is a somewhat abridged version of our usual production diary posts format, this time outlining the production of a rather complex sequence for the fulldome show "Force Five." Hopefully everyone reading this post can gleen something that will help in their own creative or production process.
INTRODUCTION:
When the Houston Museum of Natural Science decided it was time to update one of its most popular shows, "Force Five," Home Run Pictures was asked to create replacement sequences for two of the most challenging topics... hurricanes and tornadoes. Both these subjects would require us to develope new techniques to fullfill what in the past had been handled with large particle systems... and resulting in very long rendering timeframes to accomplish in the fulldome format. This "Inside the Production" post will cover our work on the tornado sequence using new tools in Autodesk Maya to accomplish the visuals.
STEP 1:
The tornado's funnel was obviously the first challenge we had to solve. Our desire was to be able to use Maya's Fluid Effects tools to create a realistic looking "twister" instead of the more obvious particle solutions used in the past. Also we desired to have good control over the movement of the twister to be able to have it "twist" over the terrain. Our favorite looking tornado was the one in the old "Wizzard or Oz" film, that even though done many years ago still has a very believable look.
There are several approaches covered in online tutorials amd in how-to books , but none of them completely provided all the necessary controls to effectively generate a twister for an extended scene of about four minutes. The Maya Fluid Effects approach would allow for shorter render times as well as a very good appearance... if we were to be successful at truely updating the look of the "Force Five" show.
Our final solution was to create a Maya Fluid Effects system that had three basic control points... an emitter, a containment volume and a movement/twisting control system. The emitter would generate the fluid material that would be rendered to look like a typical twister, and a series of curves (Volume Curve Field in Maya) would confine the fluid in the shape we desired. For control of the twisting motion we manilulated the containment field with a Maya Hair system curve... the hair having built-in dynamics with a constraint at the top and bottom for our control needs. A rotating vortex force was added to spin the entire simulation.
A similar Fluid Effects system was added at the bottom to generate a swirling dust vortex, but without the containment field or hair dynamics since it was desirable that the dust generated by the funnel would be randomly thrown around. The color was also changed to depict the dirt being picked up by the twister. By moving the entire container group as well as the top and bottom constraints of the hair, we were able to move the tornado around our scene, hitting or missing trees and buildings as desired.
STEP 2:
Now that we had a workable funnel rig, we then needed to place it in a scene with terrain, trees, buildings and a cloud layer above. A combination of methods were employed to accomplish this. At times 3D models were constructed, other times painted images textured onto appropriately positioned planes and cylindars were used. Our main cloud formation was again created using Maya's Fluid Effects system and placed in a large volume just above the top of our funnel. The colors of the clouds and the funnel were matched to blend together using some transparency variation scripts.
In the following scenes in the sequence, the clouds are Maya Fluid Effects, the ground terrain, vehicle, structures and telephone poles are 3D geometry and the background is a painted texture on several large cylinder shapes in the distance.
Several layers of particles to represent dust, dirt and debris were also added to finish the effect. All these layers were composited in Adobe AfterEffects. At times the funnel, bottom dust, clouds and other elements were rendered separate to have more control on the final look. Everythiung rendered quickly, much faster then with a particle approach.
For one scene a flock of birds reacting to the approaching twister was added in, motion created as particles somewhat randomly following a curve path and replaced with simple polygonal bird geometry. In another, Maya Paint Effects trees with particle leaves swirling in the vortex were included. And in another lightning and hail.
STEP 3:
The most complex challenge was the closing scene where a house is hit by the twister and is torn apart. It was accomplished by a combination of dynamically controlled forces and hand animated debris to allow for some creative control over the look of the motion. The geometry of the house was split into hundreds of "shards" that the dynamic forces could then throw around in spiraling motions. All element's positions were cached on a frame-by-frame basis for quicker rendering and allowing for multiple computers to accomplish the final rendered layers. Both particle-based and Fluid Effects dust clouds was added in to create a feeling of depth.
STEP 4:
During the creative development of the sequence, it was determined that we would need some sort of cut-away scene to insert between the various scenes. Attempting to do this as one continious sequence brought back all the issues that made it difficult to accomplish years ago when large quantities of particles were the only pipeline... just too much happening. The storyline added in two people in a vehicle as tornado spotters. We could cut into the interior and then back out again without a "jump cut" effect. jarring the audience as we changed camera views.
The interior scenes were rendered and "outside" views were rendered to best fit the sequence's progression. These were then composited in to allow for a smooth transition between scenes with differing camera viewpoints... always attempting to view the twister from the most dramatic point of view.
That's a quick description of the production pipeline for the tornado sequence in the "Force Five" show. Total production time was about four months from concept to delivering final rendered frames.
Click on the link below to see a Quicktime® movie of the complete sequence complete with audio sound effects from the show.
TC
