So what is Motion Capture, Performance Capture or Mocap? In it’s simplest form it is the recording of the motion of an object by a computer using a series of sensors. As a process it is the planning, recording and integration of that data – It’s the people in Lycra suits covered in shiny ping-pong balls you see in the “Make of Section” of your DVDs.
In simple terms motion capture systems can capture the motion of anything you can attach a sensor to. Attaching the sensor is the easy bit, applying the data to your model convincingly is the tricky part.
All motion capture systems collect some sort of data from the object the sensors are attached to. Optical systems calculate the relative position of each marker. Inertial systems measure the acceleration and rotation of each sensor.
In it’s raw form motion capture is simply a set of values for each sensor at a specific time, so you need a way to transfer this data on to your object inside a computer. If you think of it like a puppet system, you need the strings to transfer the movements of the performer on to the puppet in the computer.
Some capture systems come with their own software for doing this –Vicon’s Blade, Motion Analysis’ Cortex, and Xsens MVN software. There are also a number of third party software solutions like Autodesk MotionBuilder and PeelSolve. Some facilities have also developed their own software solutions like Giant Studios.
The actual capturing of the motion or performance is only the middle part of the process though. Before you start capturing you need to decide what you’re going to capture and how you’re going to capture it.Once the capturing is done you’ll need to map the data to your character and integrate it in to your pipeline.
Sounds simple enough? Except within each one of those steps there are a number of other tasks to contend with like
- Creating move lists
- Arranging shoots
- Rigging characters
- Capturing the data
- Cleaning up the data
- Mapping the data to your character
- Editing the data
As you can see the actual capturing of the motion is only a small part of the whole motion capture process. It should feel more like the easiest part as to make the whole process as painless as possible you will need to plan everything – and I do mean EVERYTHING! It really is one of the fail to plan, plan to fail things.
While we’re here – and because people always ask – what’s with the Lycra outfits? The markers or sensors are placed in precise locations on the body to capture it’s movements. They needs to stay fixed to those locations to accurately record the movement of the performer. If the performer wears loose fitting clothing the markers will move around independently of their body. You would be capturing the movement of the clothing not the movement of the performer. Although there is still a small amount of movement with the Lycra suits it’s a lot less than a sweatshirt and jeans. So for now it’s black Lycra suits – at least the cameras cant see you, for that it’s even worse!