Jed Swartz - Five Years on Mars

While audiences are used to seeing virtual characters and worlds beyond their imagination created using computer graphics, the use of CG for medical, scientific and industrial visualization is often forgotten. That is not the case with Jed Schwartz, the owner of New Hampshire based Jed Schwartz Productions (JSP). His studio specializes in visual effects and 3D animation for visualization projects and has an impressive client list including companies such as Pfizer Pharmaceuticals, Discovery Channel and NBC.

In this recent project for the National Geographic Channel, Jed helps chronicle the adventures of the Mars Rover Spirit as it tackles the alien Martian terrain. His team was tasked with compiling close to forty shots totaling twelve minutes in length that re-enact the Spirit forging its way across the rocky, desert-like surface. They were required to create a meticulously detailed photo-realistic recreation of this landscape especially those troublesome obstacles which from time-to-time hold up the exploring rover.

In order to precisely generate the red planet’s terrain, Jed sourced out numerous satellite and digital elevation maps for reference from the USGS Planetary Web Server. He then compiled these maps into a mosaic, a monster satellite image weighing in at 20000 pixels x 16000 pixels, providing him with a perfect Digital Elevation Model (DEM).

In order to convert this imagery into 3D terrain that could be navigated by the rover, Jed shared his production challenges with Side Effects Software’s support department. Together they developed a procedure for controlling the elevation of grid points based on the values of the DEM. Senior Technology Consultant Jeff Wagner prototyped two Houdini Digital Assets for this project – Displace by Map and Color by Map. Each of Jeff’s assets was implemented using VEX operators and included features that very useful for controlling elevation and the color detail applied to the geometry.

“Being able to work with production specialists at Side Effects while planning out a project allows us to find the most efficient technique possible,” says Jed. “The two assets built by Jeff gave us the right toolset to get the job done.”

The terrain was grouped out and then regions that were subjected to extreme close up shots were subdivided and modeled in finer detail using sculpting tools to match the reference images from NASA. As he worked, Jed created custom parameters to allow for quick toggling between the proxy geo and the maps. This made it much easier to switch between a very fast interactive model for blocking camera moves and animation and high-res output for rendering.

Dan Maas of Maas Digital had produced the alternate "Opportunity" rover shots in the program, he supplied his Rover data from previous projects to JSP. David Gregg of Digital Magic, JSP’s partner in this project imported the Rover data into Maya for shading and lighting the Spirit model, then the model was imported into Houdini using FBX files for rigging and animation. There were over a thousand separate parts in the model, each one in its own object grouping. The team decided to write a Houdini script that would optimize the geometry by consolidating large groups of objects together and writing them out to a more manageable set of .bgeo files. By reducing the number of separate objects to a few dozen it was easier to set up a hierarchy and set of controls to handle the movement of the various panels and devices on the rover, especially the wheels and steering.

Jason Simmons who got involved with JSP for this project was responsible for rigging the model to roam freely on the Houdini generated terrain. He developed a rigging system that would keep the rover’s wheels on the ground while the suspension responded to every bump hill and rut in the terrain. The animators would require independent control over each of the six wheels but also set up the hierarchal motion to be automated as much as possible.

Using Houdini's standard bone objects and IK solvers along with a few other constraint and hierarchy tricks, the team built a rig that would track the wheels over the ground terrain geometry with detailed interaction of the rover's mechanical parts. Suspensions and wheel assemblies would flex and rotate in a correct fashion, and a CHOPs network with some basic math expressions were used to spin the wheels accurately whenever they were in contact with the ground.

This setup also included a complex mechanism to handle correct yaw as the rig traveled over uneven terrain; not only did the wheels and suspension tilt forward and back when negotiating bumps or hills, it also needed to bank from side to side without any shearing or lateral sliding.

They also built in the ability to override and disable the automatic features of the rig for a few shots depicting the failure and malfunction of one of the rover's wheels and steering mechanisms. The rig was then packaged into a Houdini Digital Asset with a detailed parameter interface with organized controls for the various sections of the rig along with a variety of display controls.

Components from the animated rover rig were used to generate tracks on the Mars surface. As the rover forged a path across Mars, it left its imprint in the surface with the tracks created by its rugged wheels.

“We generated motion trails from each of the six wheel positions, and using that together with the steering orientations, we generated tire tread patterns that we could project onto the ground surface and render as animated displacement maps while other mattes and elements were used in compositing to create the realistic tracks left behind by the rover,” says Jed. “Additional effects were also generated in Houdini, including some ambient dust and some small particle animations and rigid body simulations to recreate pebbles and bits of gravel displaced by the rover throughout the sequence"