Fig. 2.

Sampling the range-image database with geometrical templates. (A) Representative scene acquired by laser range scanning (only a small portion of the full wide-field image obtained by the scanner is shown here). A true color image (Upper) and the corresponding range image (Lower) are shown; the distance from the origin of laser beam to each point in the range image is indicated by color coding. Black areas (sky) are points in the scene from which no laser reflection was recorded. (B) The pixels in a 2D image projected from a region of the 3D scene in the database are represented diagrammatically by the grid squares. The black dots indicate the reference-line template, and the red dots indicate a series of templates for sampling a second line oriented at various angles with respect to the reference line. (C) The set of white dots indicates a valid sample for a reference line in this example (i.e., the set fulfills the geometrical criteria described in Materials and Methods). Blowups of the boxed area show examples of a second template that was successively overlaid on the same area of the image to sample for the presence of a second straight line in different orientations (the second template in each of these cases is also a valid sample).