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 into a synthesized depth image, the synthesized depth image including a synthesized pixel of interest having a synthesized depth value; receiving an observed depth image of the human target from a source, the observed depth image including an observed pixel having an observed depth value and a same pixel address as the synthesized pixel of interest; classifying the synthesized pixel of interest with a refine-z pixel case if the synthesized depth value does not match the observed depth value and an absolute difference between the synthesized depth value and the observed depth value is less than a predetermined threshold; computing a refine-z force vector for the synthesized pixel of interest, a magnitude of the refine-z force vector being based on the absolute difference between the synthesized depth value and the observed depth value such that the refine-z force vector increases in proportion to the absolute difference between the synthesized depth value and the observed depth value; and mapping the refine-z force vector to one or more force-receiving locations of the machine-readable model representing the human target to move the machine-readable model towards the human target in the observed depth image.