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; rasterizing the machine-readable model of the human target as part of a synthesized depth image including a synthesized pixel of interest; receiving an observed depth image of the human target from a source, the observed depth image including an observed pixel corresponding to the synthesized pixel of interest; and if an observed depth value of the observed pixel is less than a synthesized depth value of the synthesized pixel of interest by more than a pull threshold amount, applying a pull force vector to a force-receiving location of the model to pull the model toward the synthesized pixel of interest; or if the observed depth value is greater than the synthesized depth value by more than a push threshold amount, applying a push force vector to a force-receiving location of the model to push the model away from the synthesized pixel of interest.