Hough transform extraction of cartographic fiducial marks from aerial photography

Abstract

Cartographic compilation requires precision mensuration. The calibration of mensuration processes is based on specific fiducials. External fiducials, around the exterior frame of the image, must be precisely measured to establish the overall physical geometry. Internal fiducials are provided within the image by placement of cloth panels on the ground at locations whose position is precisely known. Both types of fiducials must be known within the pixel space of a digitized image in order for the feature extraction process to be accurate with respect to delineated features. Precise mensuration of these fiducials requires that a cartographer view the image on a display and use pointing devices, such as a mouse, to pick the exact point. For accurate fiducial location, the required manual operations can be an added time-consuming task in the feature extraction process. Interactive tools which eliminate the precise pointing action for the operator are described in this thesis. The operator is required only to "box-in" the fiducial, using a simple drawing tool, select the fiducial function, and the software of the tool returns the precise location of the fiducial.