An Application of Stereophotogrammetry in Investigating Rock Discontinuity Orientation

ABSTRACTPhotogrammetry was initially confined to the measuring of terrestrial or ground photographs for map-making purposes, but it is applicable to all sciences that depend on reliable geometric measurements of physical quantities in a fixed or transitory state. Whether stereophotogrammetry was a possible and practical method for investigating rock discontinuity orientation data was the main discussion point of this paper, and the topic was broken into several parts as follows. Firstly, the details of obtaining rock discontinuity orientation data by stereophotogrammetric methods were described, and the advantages of the stereophotogrammetric method were discussed. Secondly, theory of stereophotogrammetry is introduced briefly. Thirdly, model test was performed following the procedure under the condition of horizontal camera direction and lowered camera direction and finally, error sources were analyzed. Finally, field test was performed to verify the applicability of the method. Two types of model tests were performed, case 1 and case 2. Model was set for its back-board to be perpendicular to horizontal plane. In case 1, photographs were taken in the horizontal camera direction, which means the camera direction was parallel to the horizontal plane. In case 2, photographs were taken in a 20° downward camera direction, which means that the camera direction was 20° lower than the horizontal plane. The roots of MSE (mean squared error) in dip for case 1 was 3.4° over 360° which is 0.94%, for case 2 was 5.3° over 360° which is 1.47% and in dip direction 1.6° over 180° which is 0.89% for both cases. In the field test, out of 32 orientation data, 24 data were in the range of measured values, while the others mostly showed an error of ±1°. Results of the model test and the field test showed acceptable errors considering the variation of measurement by a conventional method.