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Drawing a Skeleton Fast From Motion Capture Data

Drawing a Skeleton Fast From Motion Capture Data. Jonathan Kipling Knight Nov 7, 2006. Introduction. Purpose Motion Capture Data Files Skeleton Formation Closed Form Solution Conclusion. Purpose. Draw an articulated framework of solid segments connected by joints.

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Drawing a Skeleton Fast From Motion Capture Data

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  1. Drawing a Skeleton Fast FromMotion Capture Data Jonathan Kipling Knight Nov 7, 2006

  2. Introduction • Purpose • Motion Capture • Data Files • Skeleton Formation • Closed Form Solution • Conclusion JKK

  3. Purpose • Draw an articulated framework of solid segments connected by joints. • Use live data capture to draw figure. JKK

  4. Motion Capture • Magnetic Trackers • Position and Orientation Transmitted • Light Dots • 3D Position if in view • Figure Tracking • Computer vision and image analysis JKK

  5. Motion Capture Session JKK 05_05

  6. Data Files • No international standard • Proprietary, semi-open formats • C3D oldest from Dr. Andrew Dainis • Bad Data • Users partially fill fields • Units incorrect • Frame rate incorrect • Signed/unsigned mismatches JKK

  7. Producing a Skeleton • Single Time Frame • Produce position, size and orientation of each segment • Markers are fixed 3D positions on segment • Orientation is included with magnetic trackers • Rotation Points are fixed on TWO segments but are not in data JKK

  8. Producing a Skeleton • How to Move Between Frames • Inverse Kinematics popular • Forward and Inverse Kinetics • Closed Form Solutions JKK

  9. Inverse Kinematics • What joint angles are needed to get to next position and orientation? • Good for filling in large frame gaps • Sometimes more than one answer JKK

  10. Inverse Kinematics Example JKK

  11. Closed Form Solution • Requires 1-3 positions on each segment • Each frame independently drawn • Quickest O(26N) • As accurate as data O(/N) JKK

  12. Segment Tree • Root segment usually hips • Leaf segments hands, head and feet • No loops Leaves Root JKK

  13. Solve Sphere at Each Joint • One marker on child produces sphere around joint relative to parent • Must know orientation of parent • 1-3 markers needed or • Magnetic trackers JKK

  14. Three Point Orientation • Three Orthogonal Axes JKK

  15. Two Point Orientation • Three Orthogonal Axes JKK

  16. One Point Orientation • Three Orthogonal Axes JKK

  17. Center of Sphere • Asymptotically Unbiased Generalized Delogne-Kåsa Method JKK

  18. UGDK • Asymptotically unbiased if measurement error estimate is correct • Fastest known O(26N) • Cholesky inverse of 3x3 matrix JKK

  19. 100 Point Comparison GDKE MLE UGDK JKK

  20. Marker Requirements • 3 Markers on root segment of tree • 1-3 Markers on all other segments • Segments with 1 Marker should have one degree of freedom (e.g.knee,elbow) JKK

  21. Break Dance JKK

  22. Salsa Dance JKK

  23. Conclusion • UGDK is fastest available sphere solution O(26N) • Asymptotically unbiased answer • As accurate as data O(/N) • 1-3 Marker requirements per segment • Provides skeleton to attach solid shape JKK

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