1. A method comprising: receiving a plurality of video frames comprising a current frame and at least one previous frame, wherein each of the plurality of video frames includes data for a corresponding image and data for a corresponding depth map; receiving a reference model comprising data from the at least one previous frame, the reference model including data representing a reference surface corresponding to at least one dynamic object captured in the plurality of video frames; processing the data representing the depth map of the current frame to produce data for a directional distance function (DDF) field that represents an area surrounding a target surface of the at least one dynamic object captured in the current frame; generating a forward transformation that modifies the data representing the reference surface to align with data representing the target surface; calculating a backward transformation that modifies data representing the target surface of the current frame to align with the reference surface, wherein the backward transformation uses at least a portion of the forward transformation; generating a transformed DDF by applying the backward transformation to the DDF; and updating the reference model with the transformed DDF to produce data for an updated reference model.