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CAMERA CALIBRATION APPROACHES USING SINGLE IMAGES OF MAN-MADE OBJECTS

Single image techniques may be very useful for heritage documentation purposes, not only in the particular instances of damaged or destroyed objects but also as auxiliary means for a basic metric reconstruction. In the general case, single images have unknown interior orientation, thus posing the fundamental question of camera calibration (as in several cases no ground control is available). To this end, the known – or assumed – geometry of imaged man-made objects may be exploited. Recovery of the three main elements of interior orientation, together with image attitude, requires the existence on the image of lines in three known non-coplanar directions, typically orthogonal to each other (from the lines, radial lens distortion might also be estimated). Several approaches have been reported for the exploitation of this basic image geometry; however, the expected accuracy has not been adequately investigated. In this contribution, three alternative algorithms are presented, based: on the direct use of the three basic image vanishing points; on the use of image line parameters; and on the direct use of image point observations. The integration of radial distortion into the algorithms is also presented. The reported results are evaluated, and promising conclusions are drawn regarding the performance and limitations of such camera calibration methods, as compared to self-calibrating bundle adjustment techniques based on control points.