Bibliography: leaves 137-156. / The purpose of this research was to identify how the distribution and availability of spatial data could be improved. This should then minimize the duplication of data and ensure a better utilization of available data sources. All decisions that are made should be based on information, and especially decisions about our natural resources should be based on geographical information - this is spatial information of our environment. Many users, however, are not aware of the spatial data available or where to find it. In Chapter 2 the literature review reports on the spatial data sources in other countries, and different methods that are used to make this data available to the users. Most of the research was done on the distribution of digital data, and not much on traditional non-digital material. The establishment of national land information systems and data sharing via the networking of databases is receiving wide attention. An investigation was done to establish the spatial data suppliers and the data users, the types of data supplied, and the requirements. Three possible methods were investigated to improve the distribution of spatial data and•to reduce the duplication of data: a comprehensive GIS with a full database; a national spatial data infrastructure (NSDI); a metadata base.

Bibliography: leaf 53. / This thesis report discusses the design, implementation and testing of a non-contact measuring tool based on the principle of stereo photogrammetry. The system uses a pair of CCD video cameras and a frame-grabber in a PC to capture the pair of images this requires. The software on the PC then measures the image co-ordinates of points selected by the user and transforms them into space co-ordinates for the points. The transformation requires knowledge of the relative positions and orientations of the cameras. This is found in a calibration stage from images of a calibration frame. The cameras are mounted on a bar, which guarantees that the relative positions and orientations of the cameras remain invariant within certain limits. This makes the system portable.

Bibliography: pages 132-135. / Transnet possesses approximately 60000 land parcels covering the whole of the South African rail network. These parcels, or polygons, will form the base map in a corporate Geographic Information System (GIS) which will be used for property administration and general railroad operations management. Accuracy requirements are high and unique coordinate values have to be determined for each polygon apex before data are input into the GIS. Railroad property portfolios are characteristically configured in long thin strips. The solution therefore has to cope with poor geometry. The method used to determine apex coordinates must be time and cost efficient, and produce acceptable levels of precision. This study examines the feasibility of using a particular mathematical model with the least squares method in the partial automation of the determination of unique points from sets of differing and, at times, conflicting cadastral data for the creation of a digital cadastral database. The approach is not a mathematically rigorous conventional survey network solution, but a pragmatic application of least squares and network principles, to suit the nature and limitations of the data.

Bibliography: pages 51-53. / This thesis reports on the design, development and testing of a semi-automated system to aid in the mapping of the interior of industrial plants. The system makes use of digital photogrammetry to assist an operator in locating and identifying components of the plants. All of the important photogrammetric theory is discussed in the text, and explained in detail in the appendices. Specifically, this system implements various algorithms used for camera calibration, object point intersection, and a method combining the two techniques. Considerable use is made of the iterative least squares method, which is the basis of many of the algorithms employed in this work. Image processing algorithms are implemented to enhance the digital images, and to ease the identification of objects in the images, and these are fully explained in the text. Adaptive least squares image matching is a method of matching corresponding points in different images and is used to ensure correspondence between points identified by the system operator. A weighted centre of gravity method is used to find the centre of target areas, and an algorithm is implemented to determine the radius, centre and direction of a pipe passing through a number of points. Various aspects of the system design are discussed and explained. In particular the requirements in terms of hardware and software are presented. In addition, the choices of the operating system and of the compiler are justified. Potential problems with the system, and possible enhancements of it are also described. Tests were performed to verify the correct operation of all of the algorithms used in the calibration of the cameras. Together with the point intersection routines, these tests calculated the position of various control points, the correct coordinates of which were previously known. The calculated point positions are compared to the known coordinates of the points to determine the accuracy of the various algorithms. Further tests were conducted to demonstrate and verify the ability of the system to measure distance in three dimensions. These tests illustrate that the accuracy achievable is approximately 0.053 of the total distance measured for an object occupying 803 of the width of the image. The system improves considerably on the method presently used in South Africa and in many industries worldwide which rely on analytical photogrammetry for the determination of object point locations. While the system suffers from reduced accuracy as a result of the use of digital cameras, this problem will become less important as technology and digital camera resolution improve. Possible enhancements include the use of more numerically efficient algorithms, and the introduction of techniques that would partially automate the identification of control points and pipes.

Bibliography: p. 101-108. / Modern geodesy utilises advanced space techniques such as VLBI to further the study of crustal motion as well as tidal and rotational deformations of the Earth. One of the parameters in the model used to determine the baseline length between VLBI stations, is the antenna axis offset. This offset is the distance between the secondary axis and the normal projection of the secondary axis onto the primary axis. For a non-intersecting axes antenna mounting, this offset is usually several metres in length. The accuracy of the offset value directly influences the total accuracy of the VLBI results. This work describes how GPS is used to determine the offset and VLBI reference point. Several algorithms for calculating these parameters are investigated and evaluated. Methods are developed to minimise the size and influence of errors. An evaluation and comparison of the results to previous independent determinations of the offset, which use different techniques and instrumentation, clearly show the feasibility of using GPS. This method has the added advantage of allowing the VLBI, SLR and GPS reference frames to be co-located.

Bibliography: leaves 64-65. / This thesis describes research and development work which led to algorithms, procedures and computer programs which facilitate the cost effective and accurate capture of geometric data. The geometric data for a Geographical Information System (GIS) at a local authority or municipality consist of a number of different data sets. These include inter alia: the cadastral information, zoning information, servitudes, building lines, the outlines of improvements and the reticulation networks and the house connection points of the engineering services. The initial capture of the geometric data appears to be deceptively simple and is often not given the required consideration. The initial data capture phase of GIS projects is usually a difficult and time consuming process. This is even more so in the case of GIS for local authorities. The reason for this difficulty is the large volume of data coupled with the high accuracies required for the cadastral base map and the engineering services. Input facilities of most commercial GIS software packages generally do not provide the most efficient means of data capture. This problem warrants the development of techniques and procedures specific to local authority GIS applications which ensure that data capture can be done effectively and efficiently. The major benefit of these procedures is that they can be implemented on personal computers with low random access memory capacity. This eliminates the need for investment in costly equipment at the initial stage of data capture in the development of a GIS. It allows the capture of data on low cost technology and the postponement of the purchase of an expensive system or workstation until the data capture phase has been completed. The lowest personnel skills required are copy typing in contrast to the traditional methods of using CAD operators who command higher salaries and require more expensive training. The system developed by the author is more productive, both in quality and volume of work produced, than the CAD approach. It also permits the delay of purchase and training on expensive GIS software and hardware, which may be obsolete by the time the graphic database is established.

Includes bibliographical references (leaves 140-147). / It has been proposed that if a vascular prosthesis is to more closely approximate the mechanical behaviour of a native vessel, it should similarly feature a multi-component structure. One of the components could be a metal support structure, similar to an endovascular stent. The objective of the project was to develop a numerical tool, using the Finite Element Method (FEM) to aid in the development and optimization of such a metallic support structure. This tool was used to simulate the behaviour of different designs under the simulated in vivo conditions. The numerical results of the predicted mechanical behaviour are then analysed.

We are living in a decade, where the use of digital images is becoming increasingly important. Photographs are now converted into digital form, and direct acquisition of digital images is becoming increasing important as sensors and associated electronics. Unlike images in analogue form, digital representation of images allows visual information to· be easily manipulated in useful ways. One practical problem of the digital image representation is that, it requires a very large number of bits and hence one encounters a fairly large volume of data in a digital production environment if they are stored uncompressed on the disk. With the rapid advances in sensor technology and digital electronics, the number of bits grow larger in softcopy photogrammetry, remote sensing and multimedia GIS. As a result, it is desirable to find efficient representation for digital images in order to reduce the memory required for storage, improve the data access rate from storage devices, and reduce the time required for transfer across communication channels. The component of digital image processing that deals with this problem is called image compression. Image compression is a necessity for the utilisation of large digital images in softcopy photogrammetry, remote sensing, and multimedia GIS. Numerous image Compression standards exist today with the common goal of reducing the number of bits needed to store images, and to facilitate the interchange of compressed image data between various devices and applications. JPEG image compression standard is one alternative for carrying out the image compression task. This standard was formed under the auspices ISO and CCITT for the purpose of developing an international standard for the compression and decompression of continuous-tone, still-frame, monochrome and colour images. The JPEG standard algorithm &Us into three general categories: the baseline sequential process that provides a simple and efficient algorithm for most image coding applications, the extended DCT-based process that allows the baseline system to satisfy a broader range of applications, and an independent lossless process for application demanding that type of compression. This thesis experimentally investigates the geometric degradations resulting from lossy JPEG compression on photogrammetric imagery at various levels of quality factors. The effects and the suitability of JPEG lossy image compression on industrial photogrammetric imagery are investigated. Examples are drawn from the extraction of targets in close-range photogrammetric imagery. In the experiments, the JPEG was used to compress and decompress a set of test images. The algorithm has been tested on digital images containing various levels of entropy (a measure of information content of an image) with different image capture capabilities. Residual data was obtained by taking the pixel-by-pixel difference between the original data and the reconstructed data. The image quality measure, root mean square (rms) error of the residual was used as a quality measure to judge the quality of images produced by JPEG(DCT-based) image compression technique. Two techniques, TIFF (IZW) compression and JPEG(DCT-based) compression are compared with respect to compression ratios achieved. JPEG(DCT-based) yields better compression ratios, and it seems to be a good choice for image compression. Further in the investigation, it is found out that, for grey-scale images, the best compression ratios were obtained when the quality factors between 60 and 90 were used (i.e., at a compression ratio of 1:10 to 1:20). At these quality factors the reconstructed data has virtually no degradation in the visual and geometric quality for the application at hand. Recently, many fast and efficient image file formats have also been developed to store, organise and display images in an efficient way. Almost every image file format incorporates some kind of compression method to manage data within common place networks and storage devices. The current major file formats used in softcopy photogrammetry, remote sensing and · multimedia GIS. were also investigated. It was also found out that the choice of a particular image file format for a given application generally involves several interdependent considerations including quality; flexibility; computation; storage, or transmission. The suitability of a file format for a given purpose is · best determined by knowing its original purpose. Some of these are widely used (e.g., TIFF, JPEG) and serve as exchange formats. Others are adapted to the needs of particular applications or particular operating systems.

Bibliography: pages 113-117. / The Department of Surveying and Geodetic Engineering at the University of Cape Town, in conjunction with the Department of Mechanical Engineering at the University of Cape Town have developed a non-contact co-ordinate measurement machine in a project called MILIMAP. The project had the following objectives : 1. To determine unique surface co-ordinates for continuous, complex objects with submillimetre accuracy. 2. The representation of the co-ordinates was to be in a format that could be utilised by a computer numerically controlled (CNC) milling machine in a computer aided design/ computer aided manufacture (CADCAM) environment. 3. The device had to use a non-contact method for data capture. The MILIMAP project was undertaken because there is a demand for co-ordinate measurement machines in industry for the inspection of objects for quality control purposes. Conventional Co-ordinate Measurement Machines (CMMs) are expensive and use a contact probe to measure the object. The contact probe measurement technique is unsuitable for the measurement of non-rigid objects such as shoes and automobile seat padding. The MILIMAP system provides a noncontact measurement technique that can be applied to non-rigid as well as rigid objects. Additional applications in the archaeological field exist for the non-contact measurement of sensitive, historical artefacts. A digital photogrammetric system was developed to measure the position of a laser dot projected onto the surface of the measurement object. This measurement system satisfied the criteria of a non-contact measurement method required for the project. The system utilised three digital CCD cameras to capture images of the laser dot projected onto the object. Image processing software, developed from existing software within the Department of Surveying and Geodetic Engineering, was used to photogrammetrically determine the co-ordinates of the laser dot to sub-millimetre accuracy on the surface of the object. A mechanical device was designed and constructed by the Department of Mechanical Engineering in order to move the laser over the surface of the object, and to rotate the object. The entire surface of the object could be measured by the system using these operations.