343 Industries Builds OptiTrack Mocap System for ‘Halo 5: Guardians’

“We went from having a painfully tiny volume to a versatile setup that puts out super clean data and allows us the space for all the tasks we need to carry out for this project. Motive tracking and solving software is simple to use and very stable. We are able to get results quickly,” said 343 Industries’ motion capture supervisor Mark Tanner. The more dynamic motions in a project such as this benefit from larger capture volumes.

OptiTrack is an optical motion capture system, which uses an array of synchronized cameras placed around the target capture volume to capture 2D images from different angles. The 2D positions are identified first, and the overlapping position data are compared to calculate the 3D positions via triangulation.

Tracking and Solving

The Prime 41 camera used for Halo 5 is the top of the OptiTrack range, chosen by 343 for its suitability for huge, even outdoor, capture volumes - high precision with a 100ft tracking range. During capture sessions, OptiTrack cameras use Motive software to collect and process the motion data.

Motive software is a 3D reconstruction and rigid body solver that uses tracking filters and constraints to fine tune object tracking. Two types of Motive software handle data streaming from the camera system - Motive:Tracker, designed to track rigid bodies, and Motive:Body, able to track both skeletons and rigid bodies.

Motive’s asset and data management systems will automatically assign rigid bodies and custom marker sets to the recordings they were tracked in as file metadata, which is kept associated within a single project folder. Motive:Tracker supports standard streaming engines like VRPN and Trackd, and users can access data at any stage in the pipeline – the 2D camera images, marker centroid data, unlabelled 3D points, labelled markers and rigid bodies.

Motive:Body, on the other hand, has calibration tools and can calibrate a skeleton or group of skeletons very quickly and gains a clear understanding of each subjects’ skeletal structure, which it uses to produce distinctive marker labels. The resulting captured data can be sent to MotionBuilder for animation. Motive:Body will export a pre-configured actor, with skeletal proportions and markers prepared for use at the end. This approach delivers extremely accurate marker labels, supporting high quality, real-time output even during close interaction between actors.

Motive:Tracker exports tracking data in CSV and C3D formats, the dedicated capture data format. Motive:Body exports CSV and C3D files, as well as FBX - Binary and ASCII, BVH and TRC. The capture data can also be streamed to other software that uses supported plug-ins and data-streaming pipelines.

Diversity of Characters

343 Industries cinematics director Brien Goodrich said, “When I’m working with actors on set, my hope is that I'm not even thinking about data, solving and animation. Our OptiTrack system affords a straightforward mocap experience that allows me and the production to focus on the performance.”

Owing to the diverse characters in the ‘Halo’ series, 343 Industries depends on motion capture to differentiate a wide range of action, from subtle movements up to full blown stunt work with actors leaping off props and performing complex grappling action. During the height of production, the mocap system was used everyday for tasks from prototyping and character concepting, to displaying keyframe animation reference and outputting final solves.

OptiTrack camera systems have sufficient fidelity to capture most human body and rigid body movements, including both subtle and fast motions. The 3D location of markers can be resolved with sub-millimeter accuracy, but it is important to determine an optimal capture volume size and camera configuration. Rigid body movement can be captured when at least three markers are visible, and facial movement and skeletons can be tracked as long as enough markers are visible. Movements that involve too much occlusion of markers may need marker and camera placement adjustment.

Real-time Visualization

OptiTrack’s Insight VCS Virtual Camera System was also used for to visualise camera work for the cut-scenes in Halo 5: Guardians.Real-time virtual camera tracking is very useful for scouting virtual locations, framing shots and rapidly iterating for new ideas on complex scenes. Camera moves and capture mocap actors can be established together in the same volume, as a natural previs technique that can’t be achieved with traditional keyframing. Pre-made animation can also be integrated into a scene and combined with live camera work.