1. A method for estimating and tracking poses of a subject, the method comprising: generating data points of the subject from a first depth image including the subject by a depth camera, the first depth image representing distances from the depth camera to different parts of the subject; grouping the data points into a plurality of segments of the data points based on, at least, depth profiles of the data points and spatial positions of the data points; grouping the segments of the data points into labeled parts of the subject based on, at least, spatial relationships between the segments and constraint conditions by: calculating a cost of assigning the segments to the labeled parts; and assigning the segments to the labeled parts where the cost is minimized; and fitting a model representing the subject to the data points using the groups to generate a pose vector representing the pose of the subject estimated from the data points.