OptiTrack Motion Capture System priced in range of small developers.
Posted March 9 3:21 AM by Rafael Baptista
One of the surprises of the show for me was NaturalPoint's OptiTrack Motion Capture system.
I'm currently in the planning stages of a console game project that will involve using a lot of motion captured animation. All of the motion capture systems I had seen up till the show start at about $50,000 for a very basic setup - and quickly reach to $250,000 or more for high resolution cameras. This puts buying a motion capture system outside the budgets for most small game developers - and certainly beyond the means of our next project.
Our plan was to rent a motion capture studio by the day. Typical cost for such places are in the range of $5000-12000 per day, and you normally have to rent the space in whole day blocks. The nice thing about this is that the mocap studio will usually have very high end equipment and comes staffed with a dedicated team of technicians. The downside is that you can't just do motion capture whenever you need to. All animations have to be planned out in advance and recorded when the studio space is available. This kills your ability to iterate quickly. If it turns out that a certain motion doesn't end up working the way you want in the game you can't just record a replacement the same day- you have to wait till your next full day session. And you end up feeling the cost of every session - which may cause you not to rerecord stuff that you probably should. Some of your creative decisions will end up being constrained by financial considerations. Another problem is that unless you are lucky enough to live right near by, you will have to fly out your animators and actors to the mocap place for each session - which can get expensive very fast.
So I was pretty excited when I ran across this little motion capture company, NaturalPoint, who was demonstrating a simple yet effective motion capture setup for $5000. That's less than the cost of one day of renting a motion capture stage. Its worth getting even if all it does is save you from renting the stage for one or two days to pick up the few animations you missed from the last major session, or even for fast iteration of prototype animations.
My concern with this system was with the radically lower price, what would I be missing? The $5000 setup is pretty minimal - 6 of their v100 cameras, recording at 100hz, at a resolution of 640x480. This is the bare minimum number of cameras to capture full body animation in a 10x10 foot capture space. Additional v100 cameras will cost less than $500.00 each.
The higher end equipment can collect data at a much higher resolution - which is enough to capture not only full body animation but also simultaneously capture facial animation. With the OptiTrack system to capture facial animations you would have to focus the cameras on the face alone in a separate pass.
The higher end systems can capture data at 200hz or more. This is necessary to properly capture fast motions like swinging golf clubs and the like. I'm not sure the OptiTrack would be appropriate for this at all. On the other hand, games run at 60hz, and typical game animations are recorded at 30hz, so OptiTrack's camera should be good for anything that doesn't need to be played back in slow motion.
The relatively low resolution OptiTrack cameras are good enough to capture movement of one or two actors in a small 10x10 capture volume. To capture in a larger volume you would need either higher resolution cameras, or many more cameras. Since the cameras communicate over USB, the OptiTrack system won't scale beyond 20 cameras. After that the USB bus starts to get saturated.
One of the most interesting features of the OptiTrack system was that the image analysis is actually done on the camera in an FPGA. So the system does not require a compute server to do image analysis. They demonstrated the system capturing motion in real time directly to a small laptop over USB. This means the entire system is highly portable.
To set up a capture volume you would need to set the cameras up on tripods around the volume. The floor needs to be fairly rigid - like a concrete floor. Like any camera based motion capture system - if the cameras shake during the capture the data will be extremely noisy. The stage would be lit with relatively dim light. Once the cameras are set up, an actor 'wands' a single marker in the center of the capture volume and the system will compute the positions of all the cameras in a few seconds.
One of the things to be careful about in buying a motion capture system is that the data you get out of it will never be perfect. You will always need an animator to clean up and smooth the data for you. If the quality of the data is low - it will take your animators longer to clean up - resulting increased costs. Then your low cost animation system won't seem like such a bargain any more. With prices this low for the system - I'm thinking we may just buy additional cameras to improve capture quality and spend maybe $10,000 on the whole setup and get 15 cameras. We will have to reserve some money in our budget to buy the leotards, the markers, lights and tripods.
The OptiTrack system really changed the way I think about motion capture.
Workshop on Network and Systems Support for Games (NetGames 2009)
