Video System to Monitor Archeological Sites Using Ground-Based Photogrammetry

Abstract

An attempt was made to investigate the state-of-the-art use of a digital and near real-time system to monitor monuments and historical sites by integrating semiautomated PC-based computer vision and stereo-photogrammetric techniques. The effects of the number and type of control, particularly three-dimensional point location and distance, on the reliability and effectiveness of camera calibration procedures using planar objects as a control facility were studied. The trends of interior and exterior calibration parameters were investigated using 25 combinations of different numbers of measured distances and 3-D control points, and with a fixed focal length for the calibrated charge-coupled device (CCD) cameras. Results showed that increasing the number of distances and 3-D control points above the minimum required control numbers had a slight effect on the values of interior geometry parameters of CCD cameras as well as on the planar object coefficients. The consistency of all test results, except those with control greater than 10 distances and 20 control points, was the major reason for choosing the minimum amount of control for calibration. Quantification of the standard error of image coordinate residuals, distances residuals, standard error of unit weight, and number of iterations for convergence of algorithms supported this result. A historical statue was mapped using single camera operation and a multiple model mapping approach to reconstruct a digital 3-D surface model and thus compute the statue's geometrical characteristics. Three stereo models of the scene were captured from different perspectives. A movable cubic control facility located in the field of view of the mapped scene was used to scale the stereo models. A digital model for the statue was constructed, along with cross sections taken at selected height intervals. The mapping and camera calibration procedures were simple and practical.