Motion capture is the practice of getting motion data from live actors performing various actions. The motion data is captured (recorded) from sensors placed at the actors' joints and extremities.
3ds Max does not perform motion capture, but it accepts motion-capture data in the most commonly used formats. You can import this data to the biped and use it as is, or combined with other motions with Motion Flow or the Motion Mixer.
Motion-capture data typically needs some adjustment before it fits your biped or animation perfectly. When you import motion-capture data, you can filter it to:
In addition, some motion-capture files come with a separate marker file, which you can use to match the biped posture to the motion-capture actor.
How Motion-Capture Data is Acquired
Motion-capture data is typically acquired by one of several means:
Optical systems are quite popular. These systems can offer the performer the most freedom of movement since they do not require any cabling. Optical systems incorporate directionally reflective balls, referred to as markers, that attach to the performer. Optical systems require at least three video cameras, each of which is equipped with a light source that is aligned to illuminate the field of view for that camera. Each camera is in turn connected to a synchronized frame buffer. The computer is presented with each camera view in order to calculate a 3D position of each marker; the resulting data stream therefore consists of 3D position data for each marker. This data is typically applied to an inverse kinematics system, to animate a skeleton.
This popular method involves the use of a centrally located transmitter and a set of receivers that are strapped on to various parts of the performer’s body. These receivers are capable of measuring their spatial relationship to the transmitter. Each receiver is connected to an interface that can be synchronized to prevent data skew. The resulting data stream consists of 3D positions and orientations for each receiver. This data is typically applied to an inverse kinematics system to drive an animated skeleton. This magnetic approach shares the same lack of occlusion problems with the audio method, but it also shares the same negative factors, such as the hindrance of cables, lack of sufficient receivers, and the limited capture area. In addition, being magnetic, the system is affected by any sizable areas of metal in the vicinity of the capture area, such as girders, posts, and so on
This is one of the early methods for capturing the motion from various parts of human anatomy. These methods include simple "on/off" type of motion-detection systems as well as complex motion-tracking systems. The latter type of prosthetic motion capture would be an ideal approach if it weren’t for the complex mechanical requirements and the performance-inhibiting qualities generally associated with such designs. However, the type of data provided can be clean, rotational data collected in real time without any occlusion problems. This method is based on a set of armatures that must be attached all over the performer’s body. The armatures are then connected to each other by using a series of rotational and linear encoders. These encoders are then connected to an interface that can simultaneously read all the encoders in order to prevent data skewing. Finally, through a set of trigonometry functions, the performer’s motion can be analyzed. These design restrictions seem to be quite difficult to overcome, and will probably limit the use of this type of device for character animation.
Acoustic capture is another method currently used for performance capture. This method involves the use of a triad of audio receivers. An array of audio transmitters are strapped to various parts of the performer's body. The transmitters are sequentially triggered to output a "click" and each receiver measures the time it takes for the sound to travel from each transmitter. The calculated distance of the three receivers is triangulated to provide a point in 3D space. An inherent issue with this approach is the sequential nature of the position data it creates. In general, one would like to see a "snap shot" of the performer’s skeletal position rather than a time-skewed data stream. This position data is typically applied to an inverse kinematics system, which in turn drives an animated skeleton.
In character studio, you can import both rotation-type and position-type motion-capture files.
Motion-capture and marker data typically have keys at every frame. Filtering motion-capture data reduces keys, simplifying the job of altering or personalizing the motion data.
Motion-capture and marker data typically have keys at every frame. Filtering motion-capture data reduces keys, making the job of altering or personalizing the motion data much simpler. You can create your own library of imported and optimized motion-capture data by saving BIP files for use with other characters or as part of a longer script in Motion Flow mode. Use a biped that has no mesh attached to it with Physique. You import the data, adjust it to your liking, and save it as a BIP file. You can also run standard BIP files through this filtering process to create loops or to extract footsteps from a freeform animation.
In 3ds Max, the CSM marker file format supports a prop bone in either or both hands (left, right, or middle). There are nine additional markers for the top, bottom, and middle of the three prop types. If character studio detects these tracks, it creates a dummy helper object.
The tools on the Motion Capture rollout on the Motion panel are typically used for working with raw motion-capture data. You can also load standard BIP files using Load Motion Capture File. For example, you might do this if you want to loop the motion.
