Visual target tracking

1. A method of tracking a human target, the method comprising:

representing the human target with a machine-readable model configured for adjustment into a plurality of different poses, the machine-readable model including a plurality of joints, including one or more magnetism joints, each joint having a three-dimensional world space position;

receiving an observed depth image of the human target from a source, the observed depth image including a plurality of observed pixels;

assigning a magnetism body part to one or more of the plurality of observed pixels;

estimating a magnetism joint position based on world space positions of the one or more observed pixels assigned the magnetism body part; and

shifting a joint of the machine-readable model toward the magnetism joint position.

2. The method of claim 1 , further comprising assigning a non-magnetism body part to another of the plurality of observed pixels and shifting the machine-readable model toward the another of the plurality of observed pixels.

3. The method of claim 1 , where assigning a magnetism body part to an observed pixel includes finding a closest bone of the machine-readable model to that observed pixel, and assigning that observed pixel a body part associated with that bone.

4. The method of claim 1 , where the magnetism body part corresponds to an arm of the machine-readable model.

5. The method of claim 1 , where the magnetism body part corresponds to a hand of the machine-readable model.

6. The method of claim 1 , where the magnetism body part corresponds to a leg of the machine-readable model.

7. A method of tracking a human target, the method comprising:

representing the human target with a machine-readable model configured for adjustment into a plurality of different poses, the machine-readable model including a plurality of joints, including one or more magnetism joints, each joint having a three-dimensional world space position;

receiving an observed depth image of the human target from a source, the observed depth image including a plurality of observed pixels;

assigning a magnetism body part to one or more of the plurality of observed pixels;

calculating a centroid for observed pixels assigned the magnetism body part;

estimating a magnetism joint position based on the centroid; and

applying a magnetism force vector to a joint of the machine-readable model to shift the joint toward the magnetism joint position.

8. The method of claim 7 , further comprising assigning a non-magnetism body part to another of the plurality of observed pixels and applying a non-magnetism force vector to the machine-readable model to shift the machine-readable model toward the another of the plurality of observed pixels.

9. The method of claim 7 , where the centroid is one of a plurality of centroids calculated for observed pixels assigned the magnetism body part.

10. The method of claim 7 , where calculating a centroid includes calculating an orthodox centroid where all contributing observed pixels are weighted equally.

11. The method of claim 7 , where calculating a centroid includes calculating a biased centroid where some contributing observed pixels are weighted differently than other contributing observed pixels.

12. The method of claim 7 , where estimating the magnetism joint position includes estimating the magnetism joint position to be a position of the centroid.

13. The method of claim 7 , where estimating the magnetism joint position includes estimating the magnetism joint position to be a position found by projecting from a known location through the centroid by a known bone length.

14. The method of claim 7 , where assigning a magnetism body part to an observed pixel includes finding a closest bone of the machine-readable model to that observed pixel, and assigning that observed pixel a body part associated with that bone.

15. The method of claim 7 , where the magnetism body part corresponds to an arm of the machine-readable model.

16. The method of claim 7 , where the magnetism body part corresponds to a hand of the machine-readable model.

17. The method of claim 7 , where the magnetism body part corresponds to a leg of the machine-readable model.

18. The method of claim 7 , where the magnetism body part corresponds to a foot of the machine-readable model.

19. The method of claim 7 , where the magnetism body part corresponds to a head of the machine-readable model.

20. A method of tracking a human target, the method comprising:

representing the human target with a machine-readable model configured for adjustment into a plurality of different poses, the machine-readable model including a plurality of joints, including one or more limb joints, each joint having a three-dimensional world space position;

receiving an observed depth image of the human target from a source, the observed depth image including a plurality of observed pixels, each observed pixel having a world space depth;

assigning a limb body part to one or more of the plurality of observed pixels;

determining to which of one or more bones of the limb body part each observed pixel is closest;

calculating a centroid for observed pixels assigned to each of the one or more bones of the limb body part;

estimating one or more magnetism joint positions for the limb body part, based on the one or more centroids associated with the limb body part;

applying one or more magnetism force vectors to each of one or more limb joints of the machine-readable model to shift the one or more limb joints toward the one or more magnetism joint positions;

assigning a non-limb body part to another of the plurality of observed pixels; and

applying one or more non-magnetism force vectors to a non-limb body part of the machine-readable model to shift the non-limb body part toward the another of the plurality of observed pixels.