Motion Capture

Perhaps by now you have realised that setting up all the poses necessary to make an animation of a character with bones is a very time-consuming process. And it is very difficult to make a motion that really looks human-like. How then do movie studios manage to do such a good job making long animations with many characters moving so smoothly and realistically? The answer is MoCap or Motion Capture.

Usually this involves a person wearing a special suit covered with strategically placed reflective balls. Several video cameras film the person as he executes the desired motion and then a computer tracks the motion of each ball and converts the motions into a computer file. This file can then be applied to a rig (a character with a skeleton or 'armature'), whether that rig happens to look like a person, a monkey or a rabbit.

Here is a representation of the whole process:

Here is a typical mocap suit. Note how clear the balls are in the light of the flash.

Here is Tom Hanks in a mocap suit, acting out the motions for his character in Polar Express:

An actor breathing life into Gollum for the Lord of the Rings:

Last but not least, here is motion capture underway for the most expensive and most successful film of all time, Avatar:

What Avatar did that no other motion capture technique had done before was to add an additional camera attached to a boom and thus to the actor's head. This camera was able to record very accurately the actor's expressions - note all the tracking dots on the actor's face. And here is a YouTube video of Avatar in production:

So, are we going to be able to do motion capture at school? I'm sorry to disappoint you, but my name is not James Cameron and I don't have a budget to match his (Avatar cost about 300 million dollars!). The good news is that some motion capture files are available free on the internet. A popular format for such files is the BVH format, and this format can be imported into Blender.

Carnegie Mellon university has professionally produced over 2500 mocap files and has kindly made them available free! They are available in the BVH format needed by Blender here:

sites.google.com/a/cgspeed.com/cgspeed/motion-capture/3dsmax-friendly-release-of-cmu-motion-database

You can also get dozens of free BVH files if you register at TrueBones.com (check the Download>Freebies link).

Hey, do you remember how I told you earlier that motion capture requires special costumes and multiple cameras? Well, check this out:

freemotionfiles.blogspot.com/2009/04/motion-capture-software.html

and also

www.renderosity.com/mod/bcs/index.php?ViewProduct=23967&AID=803

Downloading free BVH files

Click HERE to download a BVH file captured from the dance on that page. (Note that shoot3D is now called iPi Soft).

HERE is a football kick.

Want more? Then download and unzip this collection of dozens of BVH files.

Importing BVH files

So how do you get these BVH files into Blender? Start Blender and delete the default cube, then do File>Import>Motion Capture (.bhv), navigate to the BVH file and press 'Import BVH'. You should now see a skeleton (armature) and if you press Alt+A or the play button in the timeline then you should see it move. Don't forget to adjust the start and finish frames in the timeline so that they match the imported motion. You will probably notice that the animation has an unexpected orientation - it is quite likely that your character is 'lying down' on the XY plane. Therefore you will have to rotate your character so that he has a normal orientation in your 3D world. You must do this in object mode, not pose mode. To rotate the selected object 90° about the x axis just type RX90 and press Enter.

Now comes the (very) hard part. The skeleton is always invisible in the rendered animation so you must make or obtain a body and then attach it to the armature. This is called 'skinning' We touched on this in the Metaman project - skinning was rather easy in that case but doing it properly with a more human-like rig is very difficult and has not been explained in this course (there are plenty of tutorials about this on YouTube and elsewhere).

Speaking of Metaman, did you notice how similar the skeleton of the dancer was to the skeleton we used for Metaman? That means you have a good chance of being able to make your Metaman character adopt the dancer skeleton without too much difficulty.

Even better than using the strange Metaman rig would be to use the Biped rig offered free on the internet by Nathan Vegdahl ('Cessen'). You can see this demonstrated on this page and you can download the files there too...