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Presentation on theme: "MOTION CAPTURE IN LIFE SCIENCES Mario Lamontagne."— Presentation transcript:


2 What is Mocap?  The creation of a 3D representation of a live performance. Understanding Motion Capture for Computer Animation and Video Games by Alberto Menache. Human Movement Biomechanics Lab

3 Applications  Entertainment Entertainment  Medicine Medicine  Arts / Education Arts / Education  Science / Engineering Science / Engineering Human Movement Biomechanics Lab

4 Entertainment: Live Action Films  Computer generated characters in live action films (e.g. Battle Droids and many others in Star Wars Prequels, Gullum in The Lord of the Rings, King Kong in King Kong) Human Movement Biomechanics Lab

5 Entertainment: 3D computer animations  Characters in computer animated files (e.g. Polar Express, Monster House) Human Movement Biomechanics Lab

6 Entertainment: Video Games  Video games by Electronic Arts, Gremlin, id, RARE, Square, Konami, Namco, and others, (e.g. Enemy Territory) Human Movement Biomechanics Lab

7 Medicine  Medicine (e.g., gait analysis, rehabilitation)  Sports medicine (e.g. injury prevention, performance analyses, performance enhancement) Gait Analysis Service Human Movement Biomechanics Lab

8 Arts / Education  Dance and theatrical performances  Archiving (e.g., Marcel Marceau) OSU/ACCAD Human Movement Biomechanics Lab

9 Science / Engineering  Computer Science (e.g., human motion database, indexing, recognitions)  Engineering (e.g., Biped robot developments)  Ergonomic product design  Military (e.g., field exercises, virtual instructors, and role-playing games) Human Movement Biomechanics Lab

10 Mocap animation  Motion capture animation is different from keyframe animation in terms of how motion is created.  Same principles apply to mocap animation & keyframe animation!  A combination of motion capture animation and keyframe animation is often used. Human Movement Biomechanics Lab

11 Keyframe animation  A keyframe is a drawing of a key moment in an animated sequence, where the motion is at its extreme.  Inbetweens fill the gaps between keyframes.  Every motion is created by animators. Human Movement Biomechanics Lab

12 Advantages of mocap animation  Faster to create (only if an established production pipeline exists.)  Secondary motions and all the subtle motions are captured -> more realism.  Physical interactions between performers and props can be captured. Human Movement Biomechanics Lab

13 Disadvantages of mocap animation  Cost.  Manipulating mocap data is often difficult -> Re-capturing or key framing a shot with bad data is often easier.  Mapping mocap data of a performer to a character with a different proportion often causes problems. Human Movement Biomechanics Lab

14 Types of mocap equipment  Magnetic systems Magnetic systems  Mechanical systems Mechanical systems  Optical systems Optical systems Human Movement Biomechanics Lab

15 Magnetic systems  Utilize sensors placed on the body to measure the magnetic field generated by a transmitter source. Human Movement Biomechanics Lab

16 Magnetic systems  Require no special lighting condition.  Sensors are never occluded.  X Require a metal-free environment. Human Movement Biomechanics Lab

17 Mechanical systems  Exoskeleton with angle sensors. Human Movement Biomechanics Lab

18 Mechanical systems  Measure joint angles (no marker ID problems).  Sensors are never occluded.  X Breakable!  X Configuration of sensors is fixed.  X Constrains on joints. Human Movement Biomechanics Lab

19 Optical systems  The cameras are equipped with infrared LED's and filters. (Filters enhance the contrast of the image.)  The cameras see reflector markers. Human Movement Biomechanics Lab

20 Optical systems  Higher sampling rate.  Larger capture space.  X Markers are sometimes occluded -> marker ID problems.  X Provide only positional data -> joint angles need to be computed. Human Movement Biomechanics Lab

21 Mocap System at HMBL  Vicon optical system –  10 high-speed MX 13 (up to 1000 fps)  Capture volume 3 x 3 2 m. Human Movement Biomechanics Lab

22 PREPARATION CAPTURE SPACE Human Movement Biomechanics Lab


24 Direct Linear Transformation (DLT)  Degrees of motion (Freedom) In 3D, How many degrees of freedom? >In mechanics, the degree of freedom (DOF) of a mechanical system is the number of independent parameters that define its configuration. Human Movement Biomechanics Lab

25 DLT  Calibration of imaging systems (2D) To calibrate is to use at least 4 known spatially defined points. Scale the film plane to the field of view x= S u and y = S v >S is defined by the distance between the control points. In 2D, the DLT is defined by the below equations Human Movement Biomechanics Lab

26 DLT  In 3D, more DoF to account for therefore the equations become more complex and we need more control points (min points are 6) x, y and z are digital coordinate of the control points (3D). L1…L11 are the DLT parameters relative to each camera. See for more explanation on DLT See Chen (1994) for the # of control points and accuracy of the reconstruction. Human Movement Biomechanics Lab

27 PREPARATION  BOUNDARY Human Movement Biomechanics Lab

28 PREPARATION  Static calibration This calculates the origin or centre of the capture volume and determines the orientation of the 3D Workspace.  Dynamic calibration This involves movement of a calibration wand throughout the whole volume and allows the system to calculate the relative positions and orientations of the cameras. It also linearises the cameras. Human Movement Biomechanics Lab

29 PREPARATION  Calibration procedure To perform the calibration: Place the L-Frame on the floor in the centre of the capture volume Select System | Live Monitors Check that each camera is viewing only the four markers on the L-Frame Human Movement Biomechanics Lab

30 PREPARATION  How good is the calibration? Residual for each Camera A residual is a measure of the accuracy of a single camera 1. They are larger the greater the distance of the camera from the capture volume and are measured in millimetres. What are acceptable residual values? Residuals should be less than 0.1% of the distance from the camera to the centre of the capture volume. For example in a capture space of dimensions 10_10_3 meters, using MCams with 12.5mm lenses you would expect residuals in the range 1 to 4mm. Human Movement Biomechanics Lab

31 PREPARATION Waving the wand There is no particular wand waving technique you should follow. You should, however, use the suggestions below as a guideline. Allow the cameras to view the wand in multiple orientations, e.g., horizontal and vertical Fill the capture volume completely Medium pace of movement Do not point the wand directly at any camera Human Movement Biomechanics Lab

32 PREPARATION What are markers? Markers are the spheres that reflect light from the strobe back into the camera. Markers come in various shapes and sizes, for example: 3mm hemispheres or 4mm spheres for facial and hand capture 9 or 14mm spheres for full body capture 12 or 20mm soft markers for capture when performing moves involving contact 25, 35 and 50mm spheres for capturing movements in very large volumes Human Movement Biomechanics Lab

33 Preparation: Markerset Human Movement Biomechanics Lab

34 DATABASE  ECLIPSE Human Movement Biomechanics Lab

35 DATABASE Human Movement Biomechanics Lab

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