Motion Capture Hardware Craig Maki and Ned Kahvo

Motion Capture Hardware Craig Maki and Ned Kahvo Motion Capture, Craig Maki and Ned Kahvo

Motion Capture: Overview l What it is and what it does. l How it works: ¡ Optical ¡ Inertial ¡ Magnetic ¡ Electro Mechanical l Motion Capture ¡ Hockey ¡ Tennis in Sports: Motion Capture, Craig Maki and Ned Kahvo 2

What it is and what it does l Process of converting physical motion to digital representation l Motion is measured and the position in 3 D space is calculated l Hardware used to measure changes l Software used to calculate position Motion Capture, Craig Maki and Ned Kahvo 3

How it works: Optical l Markers are placed on the actors ¡ l Cameras used to record movement ¡ l Number of markers varies by application/accuracy Generally 8 or more cameras used (depends on size of scene; high-end studios use ~70) Software detects the markers and triangulates the position of each visible marker relative to camera position Motion Capture, Craig Maki and Ned Kahvo 4

Optical: Markers l Passive Markers ¡ Retroreflective coating l Shines back the light sent from a light source beside the camera (like reflectors on a bike) l Active Markers ¡ LEDs used instead of reflectors ¡ Camera filters all light except for the LEDs (IR) ¡ Synchronized LEDs flash one at a time (at high speed) this makes identifying LEDs easier Motion Capture, Craig Maki and Ned Kahvo 5

Optical: Active Markers l RF receiver is worn on the actor l Used to synchronize LED flashes with cameras’ frame rate l 1 LED visible per frame(s) ¡ Allows faster processing ¡ Requires high speed cameras Motion Capture, Craig Maki and Ned Kahvo 6

Optical: Cameras l Special ¡ High l speed 480 FPS ¡ High l resolution 3600 px X 3600 px (12 -13 MP) ¡ Large l cameras Field-of-View (FOV) 60º FOV Motion Capture, Craig Maki and Ned Kahvo 7

How it works: Inertial l Uses accelerometers and gyroscopes to measure movement ¡ Think Wii Remote with higher accuracy The more sensors used, the better (more human) the results l Inertial provides 6 Degreed of Freedom (6 Do. F) 6 Do. F: l Sensitive to within 1º of rotation -translate X, Y, Z l -pitch, yaw, roll Motion Capture, Craig Maki and Ned Kahvo 8

How it works: Magnetic Sensors on the actor measure lowfrequency magnetic field created by the source l Control Unit correlates the locations of the sensors and source within the field l Benefits: l ¡ ¡ l Markers can not be occluded Fewer markers required Drawbacks: ¡ Interference caused by steel (in building) or other electronic devices (like monitors) Motion Capture, Craig Maki and Ned Kahvo 9

How it works: Electro Mechanical l Exoskeletal suit is worn by actor ¡ ¡ ¡ Aluminum or plastic rods connect multiple potentiometers which simulate joints Gyroscopes on hips and upper back used to measure rotation Change in voltage is measured (analog to digital) and position is calculated Motion Capture, Craig Maki and Ned Kahvo 10

Motion Capture in Sports l Fox. Trax Hockey Puck Americans cant follow a hockey puck, so a streak was added. Motion Capture, Craig Maki and Ned Kahvo 11

Fox. Trax Hockey Puck l Standard Hockey Puck ¡ Hollowed out and circuit board placed inside ¡ Shock Sensor ¡ Infrared Emitters ¡ Internal Battery (10 -30 minute duration) l Puck emitted infrared pulses that were detected by 20 different pulse detectors and 10 modified IR cameras located in the rafters. Motion Capture, Craig Maki and Ned Kahvo 12

Fox. Trax Hockey Puck Shuttering of IR cameras synchronized with pulse detectors l Each IR camera had a 486 -66 PC to process the video locally l These computers then transmitted the coordinates of the puck to an on site production trailer. l This trailer (called the ‘Puck Truck’) used the coordinates to apply a CG trail on the puck, which was then broadcast to the viewers at home. l Motion Capture, Craig Maki and Ned Kahvo 13

Hawk-Eye in Tennis l Does not need to modify the ball to track it. l Uses the principles of triangulation using visual images and timing data from 4+ high speed cameras (60 fps or higher). Motion Capture, Craig Maki and Ned Kahvo 14

Hawk-Eye in Tennis l On each frame ¡ System identifies the ball in every image sent from each camera ¡ Calculates the position of the ball in 3 D space by comparing each image. ¡ This is done for every instant of time to create a path of the ball in 3 D space. l System can predict the path of the ball and where the ball will strike the ground using physics. Motion Capture, Craig Maki and Ned Kahvo 15

Hawk-Eye in Tennis l l l System is set up before each match with the bounds of the playing area and the rules of the game, thus allowing it to make accurate calls (within 2 -3 mm) It uses 4 -6 high speed cameras set at different locations around the court. Each camera feeds into a high speed video processor which runs the ball tracking analysis. 3 D coordinates are then passed to a central computer which runs the physics algorithms. Data is then stored into a database and can be used in recall situations or to track player stats (shot percentages, etc. ) Motion Capture, Craig Maki and Ned Kahvo 16

Hawk-Eye in Tennis Motion Capture, Craig Maki and Ned Kahvo 17

References l l l l l http: //www. metamotion. com/motion-capture. htm http: //entertainment. howstuffworks. com/king-kong 2. htm http: //www. metamotion. com/Phase. Space/optical-motion-capturecameras. html http: //www. intersense. com/Inertia. Cube_Sensors. aspx Johnny Lee’s Wiimote Projects: http: //johnnylee. net/projects/wii/ http: //www. metamotion. com/motion-capture/magnetic-motion-capture-1. htm http: //www. metamotion. com/gypsy-motion-capture-systemmocap. htm http: //en. wikipedia. org/wiki/Fox. Trax http: //en. wikipedia. org/wiki/Hawk-Eye Motion Capture, Craig Maki and Ned Kahvo 18