The mensuration of textured surfaces using close-range digital photogrammetry for applications in industry

Hoffa, Pierre Geoffrey John

The mensuration of textured surfaces using close-range digital photogrammetry for applications in industry

Thesis / Dissertation

1996

Abstract

The mapping of rock surfaces in the open cast mining industry is of importance in assessing the fragmentation distribution of blasted rock, as well as for the profiling of vertical rock faces. This thesis reports on the development of a close range digital photogrammetric surface measurement system for the semi-automatic measurement of rock faces in open cast mining environments. The system, designed for use by nonphotogrammetrists, allows for a rapid and simple field component of the photogrammetric process. This ensures that the system, although relatively costly to set up in terms of camera and computer equipment, is relatively inexpensive to run. Various· photogrammetric and image processing algorithms were investigated and compared. Of particular note is a comparison of a number of techniques for determining approximate exterior orientation parameters of the images of the rock surface. An orientation method based on the collinearity equations, was found to be suitably robust for use in the measurement system. An investigation into the suitability of various interest operators, for extracting points of interest on textured surfaces, was carried out. The Canny edge operator proved to be the most suitable in terms of selecting a large number of well distributed points, that are representative of the surface. Image restitution was carried out by means of a fre·e network bundle adjustment. Multi-photo geometrically constrained matching with multi-image correlation was used to determine the conjugate positions of the extracted interest points. Many of the algorithms described in this thesis can generally be applied to the measurement of any surface containing sufficient texture. Three test surfaces were successfully mapped. The results indicate that the system is capable of relatively high accuracies. Using a Kodak DCS 420 still video camera to capture the images, the average relative precision in the XY plane was of the order of 1: 15000, and for the depth 1 :7000. When a low cost, 'off the shelf' ITC CCD video camera was used for image acquisition, the relative precision in the XY plane was approximately 1 :4500, and 1 :2600 in the depth. The still video camera was found to have significant practical advantages over the CCD video camera.

Keywords

Surveying and Geodetic Engineering

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