1. A computer readable storage device comprising computer readable software embodied thereon for programming at least one processor to perform a method for modeling a pose of articulated body portions of an object, the method comprising: obtaining depth pixels of the articulated body portions in one or more frames; processing the depth pixels of the one or more frames to identify the articulated body portions of the object; accessing a model, the model comprising articulated body portions corresponding to the articulated body portions of the object; matching the articulated body portions of the model to the identified articulated body portions of the object to provide an initial match; evaluating an extent to which distance constraints are violated in the initial match by the articulated body portions of the model, the distance constraints comprise constraints on distances between joints of the articulated body portions of the model; and adjusting the model in an attempt to satisfy the distance constraints, including adjusting a length of at least one of the articulated body portions of the model based on the extent to which the distance constraints are violated, wherein: the distance constraints constrain at least two of the articulated body portions of the model to be arranged end to end; the evaluating comprises evaluating an extent to which the at least two of the articulated body portions of the model are arranged at least one of: further than end to end in the initial match, or closer than end to end in the initial match; and the adjusting a length comprises at least one of: (i) lengthening the at least two of the articulated body portions of the model according to the extent to which the at least two of the articulated body portions of the model are arranged further than end to end in the initial match, or (ii) shortening the at least two of the articulated body portions of the model according to the extent to which the at least two of the articulated body portions of the model are arranged closer than end to end in the initial match.