HOUGH TRANSFORM EXTRACTION OF CARTOGRAPHIC CALIBRATION MARKS FROM AERIAL-PHOTOGRAPHY

Cartographic compilation requires precision mensuration. The calibrati on of mensuration processes is based on specific fiducials. External f iducials, around the exterior frame of the image, must be precisely me asured to establish the overall sensor geometry. Premarked ground poin ts are provided within the image by placement of panels on the ground at locations whose position is precisely known. Both types of registra tion marks must be known within the pixel space of a digitized image i n order for the feature extraction process to be able to be accurate w ith respect to delineated features. Classical mensuration of these tar gets requires that a photogrammetrist view the image on a display and use pointing devices, such as a mouse, to pick exact points. We have d eveloped interactive tools which eliminate the precise pointing action for the operator. In this paper we will discuss the theory of the ana lysis used by the tool and present examples of operation.