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What Is 3D Motion Tracking?

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  • Written By: Alex Newth
  • Edited By: Angela B.
  • Last Modified Date: 11 November 2016
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Three-dimensional (3D) motion tracking is the act of capturing motion data from actors and actresses. This is similar to filming a person moving around, but the difference is that, instead of footage that can only be played back, 3D motion tracking records the movements so they can be applied to 3D rendering programs. Performing the capture requires special hardware, such as suits and tiny tracking units, but some systems just need a camera to capture the motion. A subset of motion capturing, called performance capture, deals with extremities and facial features.

The act of 3D motion tracking is similar to filming people moving around, but the difference is in how the information is handled. With filming, the footage can only be watched, while motion capture is a digital model of the motion that can be applied to 3D figures on a computer. This is most often used by the movie industry when creating 3D animated films or when computer-based models require intricate movement. Motion tracking also is used by the military to build virtual exercises and by engineers to control machines.

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Special hardware is required to perform 3D motion tracking. In the past, actors and actresses were fitted with suits and small tracking units, and a camera tracked their movement. This hardware is still used frequently, but more advanced systems are able to capture motion data without the need of trackers, known as markerless tracking. A special camera is still needed to translate all movements into digital signals and information.

The practice of 3D motion tracking deals with how the limbs and torso move, but not the finer details of human movement. For finer details, performance capture is used. This type of tracking obtains data from finger and facial movements, so artists controlling the 3D model have intricate data about these movements. Without this information, artists have to create facial expressions and finger movements from scratch, which can lead to awkward expressions or stiff hands and fingers.

Before 3D motion tracking was available, animated film artists in the past used a similar system, called rotoscoping, to track motion. Actors and actresses were filmed performing movements and speaking lines according to the script. Artists would then take the film and draw over each frame individually. This resulted in more realistic animation, because all the movements were based on real people. Most major animation companies, before the advent of the 3D motion tracking, used rotoscoping.

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miriam98
Post 4

@NathanG - I’ve seen some rotoscoping films and in general I like them, so long as the motion is not totally fluid.

Years ago I watched these television commercials for a major brokerage house. The commercials featured investors talking about their investment decisions, and all the investors were rotoscoped. But they were totally fluid!

It didn’t look like an animation in any sense of the word, and to me, it lost its appeal and came across as rather gimmicky. Regular cartoon animations are not that fluid; rotoscoping should aim for that standard to keep it looking like it’s not just warmed over video.

NathanG
Post 3

I’ve done some video editing at home but have never attempted to do anything with motion tracking. I know some of the software available for that stuff is very high end, and of course you need the hardware too, to attach to the actor.

However, I did try my hand once at rotoscoping, which the article describes and which preceded motion tracking. I had my son do a few dance moves in front of the video camera. I then went into my video editing software and traced, frame by frame, over the video image.

Yes, it was tedious, and I didn’t produce more than 30 seconds of footage when I was done, but in the end, I had an interesting “animation.”

manykitties2
Post 2

I would have to say that Gollum from the Lord of the Rings movies is my favorite character to be created onscreen using motion capture data. His face and body language was just as expressive as any flesh-and-blood actor and he still holds up pretty well even though the movies are quite a few years old now.

I also liked Dobby from the Harry Potter films because he had that same sort of relatability that Gollum did. With such expressive fake characters I wonder how many more memorable characters motion tracking software is going to create for audiences to enjoy.

letshearit
Post 1

I know that motion capture technology is still considered very advanced, but I would be interested in trying to utilize it in a short homemade film if possible. Does anyone know what the best motion tracking software is, and if I need to invest in a special motion capture camera or anything like that?

The first motion capture character I really remember was Jar-Jar Binks from "The Phantom Menace" but I saw the film again recently and the effect already looks kind of dated and unconvincing against the special effects of today, and it hasn't even been that long. It would be great if I could do a simple project on my own that looked even half that good though.

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