Browsing by Author "Ruther, Heinz"

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    A Comparison of Close-Range Photogrammetry to Terrestrial Laser Scanning for Heritage Documentation
    (2013) Ruther, Heinz; Smit, Julian Lloyd; Kamamba, Donatius
    This paper describes the photogrammetric and laser scan survey of an excavated section of the Laetoli hominid track-way in Tanzania. The survey was designed to allow for comparison to a prior detailed survey of the track-way carried out in 1995, and serves as a means to compare terrestrial laser scanning with close-range photogrammetry as survey methods for heritage documentation. Each hominid footprint in the track-way was photogrammetrically recorded using a rigorous multi-image controlled configuration. In a separate process a laser scanner was used to scan the entire track-way as well as the individual footprints. The data for the comparison and track-way / footprint shape assessment were a photogrammetrically generated point cloud and a 3D model (established in 1995 and 2011), as well as a laser scan point cloud acquired in the 2011 survey. The results showed a high agreement between the laser scan and the photogrammetric data captured in 2011. These two survey processes are entirely independent of each other, the results can be accepted as entirely objective and the excellent agreement between the data can serve as quality control, confirming that the footprint point clouds were captured with an external accuracy of approximately 0.3 to 0.4mm. Standard deviations which are internal precision measures, and typically optimistic, show an individual point accuracy of 0.1 to 0.2 mm. The accuracy for the full laser scan track-way survey was in the order of 1mm.
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    The mensuration of textured surfaces using close-range digital photogrammetry for applications in industry
    (1996) Hoffa, Pierre Geoffrey John; Ruther, Heinz
    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.