An image of a physical environment is acquired that comprises a plurality of pixels, each pixel including a two-dimensional pixel location in the image plane and a depth value corresponding to a distance between a region of the physical environment and the image plane. For each pixel, the two dimensional pixel location and the depth value is converted into a corresponding three-dimensional point in the physical environment defined by three coordinate components, each of which has a value in physical units of measurement. A set of edge points is determined within the plurality of three-dimensional points based, at least in part, on the z coordinate component of the plurality of points and a distance map is generated comprising a matrix of cells. For each cell of the distance map, a distance value is assigned representing a distance between the cell and the closest edge point to that cell.