1. A computer-implemented object recognition system, comprising: a processor configured to receive a depth image representing an object, use a classification tree to recognize, from the depth image of the object, a visible object part and a hidden object part, and construct a volume of the object in a single data space, based on the recognized visible object part and the recognized hidden object part, wherein the constructing of the volume is based on a relative depth value stored in a leaf node of the classification tree.