There are four main applications for motion tracking technology use. Following is a general discussion of each application.
1.) Video Games – this is typically the simplest motion capture process from a marker placement requirement. Video game producers typically only require motion influencing mocap data. Thus, stringent marker placement protocols are typically not required as the output motion data is typically filtered and smoothed so that it can be used to drive character animation models. The accuracy requirements of the underlying motion can vary considerably based on the video game. Motion capture subjects typically where a velcro suit and reflective markers or LED markers are applied to the suit. Most video games don’t require high speed movements and that is not much of an issue. Sports games do require some higher speed movements, however they are typically performed at sub-maximal speeds compared to elite level performance measures. I have been in video game shoots and they are not nearly as detailed or performed at maximal speeds of an elite level sports performance analysis. Almost all video game mocap sessions are also performed indoors and environmental conditions are not really an issue.
2.) Hollywood Animation – while this application is very similar in many ways to video games, I differentiate the two as Hollywood motion tracking requirements are typically much more demanding. The main reason for this is that Hollywood has much bigger budgets, and also more time, to create more realistic and “life-like” character animations. Hollywood requirements have really pushed the envelope in terms of motion capture use, such as multiple subject captures requiring a large number of cameras, environmental considerations such as capturing in the rain or mud, as well as subjecting the markers to more physical demands in outdoor environments. Hollywood motion capture sessions are really more performance capture sessions as they really want to capture the subtleties of the actor including much finer detail of the face and hands. The following link provides a very good review of the use of motion capture in Hollywood. The 2014 release of the Dawn of the Planet of the Apes really pushed the limits of motion capture and shows how far it has progressed in a very short time.
3.) Gait Analysis & Clinical Research Studies – I consider clinical biomechanics studies more demanding than character animation applications because of the requirement for higher accuracy joint kinematics. Character animation programs will often smooth the data at the expense of some accuracy in the underlying joint kinematics. However, clinical research studies require higher accuracy in the measured joint kinematics as the underlying musculoskeletal motions are often the interest of the research studies. There are obviously character animation studies with multiple subject captures that may be considered more demanding in their capture requirements compared to a lower limb gait analysis study. The distinction I am making is strictly from the data collection methodology utilized in these studies. Orthopedic and clinical gait analysis studies have very strict collection requirements as accurate joint kinematics are required for subsequent clinical analysis to determine the best course of treatment.
4.) High Speed Sports Performance – while these types of studies are very similar to the clinical research studies such as gait analysis in terms of the importance of marker placement protocols, they are much more demanding because of the higher angular velocities of the joint segments involved. This is especially true for any type of sports performance that involves any overhead motion, as the shoulder joints have the greatest mobility in the human body. Thus, special considerations need to be made for marker types and placement, number of cameras and placement, and skin motion movement as muscles contract more powerfully. Most early sports performance studies were all performed indoors. Because of that, there were always claims that these laboratory sports performance studies never truly replicated real-life performance due to the sterile environment of a lab and having markers, sensors, and/or wires strapped all over the subject. But with time, a lot of these concerns have been diminished as technologies have improved and process have been optimized to make the sports performance movements as natural as possible. We even see more and more sports performance studies being performed outdoors in a more natural setting. The following video from the Nike Sports Research Lab (NSRL) provides a very good example of the many different high speed sports movements that can be studied with modern technology.