Browsing by Subject "Surveying"
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- ItemOpen AccessAssessing target centring algorithms for use in near-real-time-photogrammetry(1990) Rubinstein, Michael; Rüther, HeinzTarget Centring Algorithms were investigated for use in the Near-Real-Time-Photogrammetry NRTP system: PHOENICS. PHOENICS, a Photogrammetric Engineering and Industrial digital Camera System, has been developed over the past three years in the Surveying Department of UCT to provide a semi-automatic system to determine three dimensional co-ordinates of surfaces and objects using a photogrammetric method. Targets are attached to an object in order to facilitate measurement of the shape, size and orientation of the object. The centre of the target uniquely defines the target co-ordinate. Target centres (from images of the same object) are used in photogrammetric models to locate the three dimensional (3-D) coordinates of the target. The accuracy of the target 3-D location is dependent on the accuracy of the target centring algorithm. A series of sub-algorithms were employed to arrive at a single target centring algorithm. Various combinations of these sub- algorithms were compared in order to obtain the optimal target centring algorithm. Three images were used to test various aspects of the target centring algorithms: their potential accuracy was tested on an image having symmetric synthetic targets their robustness was tested on an image having targets with artificial blemishes their performance in a real (noisy) environment was tested on an image with real targets on a control frame, captured by PHOENICS. When the target centring algorithms were run on the three images, target location with an accuracy of from 1/10 of a pixel for real images, to 1/1000 of a pixel for ideal synthetic targets was obtained.
- ItemOpen AccessThe comparison and evaluation of different mathematical models for deformation analysis(1984) Goullee, Robert Jules; Rüther, Heinz; Jackson, JIn the analysis of deformations using geodetic techniques, the errors in point positions due to observation errors must be distinguished from movements due to actual deformation. A number of models are available, which offer solutions to this problem. In this study, four of such methods are described and compared: 1. Method using Invariant Functions. 2. Method using Direct Comparison of Co-ordinates. 3. Method using Direct Differences. 4. Method using Niemeier's Comparison of Co-ordinates. The introduction of "false" deformations, caused by errors in translation, rotation and scale, is a very real problem which may be eliminated by processes such as the use of invariant functions (distances and angles) and the sound construction of constraint points. Niemeier's solution to this problem is the use of a free network adjustment which forces the new network into a best fit of the provisional co-ordinates, which generally would be the final co-ordinates of a previous epoch. Although the model advocated for the first three methods above is the minimum constraint adjustment, the free network adjustment may also be used. Similarly, the minimum constraints technique may be employed for Niemeier's method, subject to some necessary modifications. The four methods have thus been compared using both adjustment techniques also. The four methods using both adjustment techniques as well as some variations of methods 1. and 2. above are evaluated using a series of nine simulated test epochs, one reference and eight other, to which known deformations were applied. From the results obtained from the various epochs, the methods are examined for reliability, accuracy and suitability.
- ItemOpen AccessThe development of a Geographic information system for environmental monitoring on the Cape Peninsula, and an assessment of the use of spot imagery for vegetation mapping(1991) Webster, Michael S; Moll, EJ; Martin, C G CThis thesis concerns the establishment of a Geographic Information System for the Cape Peninsula and the use of SPOT satellite imagery to map land cover classes. The former is seen as a necessary tool to promote judicious conservation management decisions for the fragile "Fynbos" ecosystem, and the latter as a convenient means of acquiring up-to-date information concerning the environment, and to monitor change.
- ItemOpen AccessThe implementation of the International Hydrographic Organisation's Worldwide Electronic Navigational Chart Data Base for Electronic Chart Display and Information Systems : the implications to sub-Saharan Africa(1996) Osei, Samuel; Martin, C G CThis report gives suggestions to sub-Saharan Africa regarding the implementation of the International Hydrographic Organisation's (IHO) Worldwide Electronic Navigational Chart Data Base (WEND) for Electronic Chart Display and Information _systems (ECDIS). The IHO, recognising the need to supply up-to-date navigational information to mariners at sea, proposes the establishment of a worldwide network of navigational information. This proposal is aimed at addressing the information needs of international shipping. However, it does not restrict any hydrographic office from developing its own data base for national shipping. ECDIS is one new technology that will improve safety at sea. It integrates the Electronic Navigational Chart (ENC) and other navigational information. Unlike the paper chart, ECDIS will select and display information that is needed at any chosen moment thereby removing clutter from the display. The mariner will only see the information that is relevant for his immediate decision-making. ECDIS is versatile, complex and a potentially important aid to navigation decision-making. It enables mariners to navigate under conditions of poor visibility and through narrow and poorly-marked channels. It has the power to process data from a variety of sources and to detect and graphically show relationships between the data. Since history requires us to look at the past and the present to be able to project into the future, the report begins by giving the background to electronic charts. The report examines the traditional paper chart and the present method of updating the chart. It looks at the information contained in the Notices to Mariners, Radio Navigational Warnings and Global Maritime Distress and Safety Systems. The responsibilities and obligations of the various professional disciplines involved in updating the paper chart are also discussed. The limitations of the paper chart are commented upon and the need for a new technology is emphasized. The procedure for updating the electronic chart is also discussed. The terms "paper chart" and "traditional paper chart" are used interchangeably and mean the same thing in this report. The second chapter examines the requirements of ECDIS. It discusses the user requirements and the minimum system configuration. Operational and performance requirements are also examined. Chapter Three discusses the Worldwide Electronic Navigational Chart Data Base (WEND). It gives a brief background to WEND and discusses the conceptual model of the organisation of WEND on regional bases. It examines a paper presented by Australia in relation to a single state WEND proposed by Norway. Since the whole process of networking the navigational information depends on technology, an in-depth treatment of the subject is carried out in Chapter Four. Issues discussed include networking and distributed system, standards and protocols in telecommunications. The design consideration for the infrastructure for a Regional Electronic Navigational Chart Coordinating Centre (RECC) is dealt with in Chapter Five. Financial and institutional issues are discussed. Technical and non-technical security measure are commented upon. Chapter Six deals with the infrastructure design for a RECC. It examines the infrastructure components, system operation and maintenance and manpower. Strategies for implementing RECC in the sub-Saharan Africa are discussed in Chapter Seven. Network development, data and system security measures are commented upon. Chapter Eight looks at the legal implications of ECDIS and WEND. It examines the elements of the legal regime and speculates on the possible changes that could be brought about as a result of the changing technology. Chapter Nine concludes the report with recommendations on a regional WEND centre.
- ItemOpen AccessPhysical geodesy, with special reference to deflections of the vertical.(1967) Loon, Joseph C
- ItemOpen AccessRelative orientation with limited control in close range Photogrammetry(1982) Rüther, Heinz; Adams, L PIn close-range photogrammetry, situations can arise in which it is difficult or impossible to establish a network of control points as required for a conventional absolute orientation procedure. The thesis investigates the replacement of the traditional control network by a few control distances measured between well-defined artificial markers or natural feature points. The measured distances must then serve to reduce deformations suffered by the photogrammetric model in the orientation procedures. All investigations are based on analytical rather than analogue photogrammetry. After a review of the concepts of rotation matrices, least squares adjustment and the generation of synthetic image co-ordinate observations, the study is executed in three major steps. A test field of high precision is established by means of space intersection and a camera calibration method for close-range cameras is developed which combines perspective projection with geodetic observations of the lens system parameters. Thus a problem inherent in many camera calibration methods, namely the exact determination of the perspective centre, is largely overcome. Deformation characteristics related to error in elements of interior and relative orientation are determined by the controlled introduction of errors into these elements. The deformations are presented in tabular and diagrammatical form. An analysis of the deformation leads to the conclusions of theoretical and practical relevance for close-range photogrammetry. As a result of the deformation analysis mathematical models are introduced which utilise the measured distances for the reduction of model deformations. The efficiency of homogeneous scaling, affine scaling and convergency correction, as applied individually and in various combinations, is tested. A mathematical formulation of the converging correction as a restraining condition in a least squares adjustment is developed for this purpose. It is shown that a convergency error is less relevant to close-range photogrammetry than generally assumed and that characteristic model deformations in close-range photogrammetry have the character of affine scale errors. Throughout the thesis algorithms are developed which make it possible to execute all computations on computers with limited memory capacity. A program sample for the relative orientation adjustment is given in Appendix IV to demonstrate the memory saving techniques. Finally the results of the investigation are applied to the survey of shoulder height of African elephants in their natural habitat. Equipment and field work are described and results reported.
- ItemOpen AccessThe use of airphoto interpretation as an aid to prospecting for road building materials in South West Africa(1964) Caiger, John HerbertTwo introductory chapters have been used to give the necessary background to the main subject-matter of the thesis. The first of these chronologizes the significant steps in the development of aerial photographic interpretation from the first recorded aerial photograph to the present day respected position of the art in both military and civilian professional circles. The second introductory chapter deals with the fundamental principles involved in airphoto interpretation and of their specific application to soil engineering mapping for road projects in Southern Africa. This is followed by the major theme of the thesis, which concerns the direct location by aerial photographic interpretation of the various classes of material used in the construction of a modern day road. Although aerial photographs have been employed in recent years for direct interpretation and interpolation of certain specific road building materials, their use in this manner has been limited to a few special cases. This thesis sets out to show that under certain conditions, which pertain in many regions of the world, airphoto interpretation can be used for the direct location of 1materials possessing particular engineering characteristics. Further, it sets out to show, that this can be done for the full range of engineering properties required of materials for all the significant layers of construction, despite the fact that the materials involved may be of widely differing composition and geological origin. The actual interpretation is based on the fundamental recognition of the elements of form, tone, and texture making up the total photographic pattern. Similar features reflected on photographs are shown to be comprised of similar materials, not merely geologically speaking, but more especially in respect of their significant engineering characteristics; it is still further demonstrated that this is applicable even when such features are situated some considerable distance apart. Variations of notable engineering importance within one and the same geological occurrence, are also shown to be identifiable on the aerial photographs. For major road projects in areas subjected to certain environmental conditions, these possibilities form the basis of a new prospecting technique, which incorporates the full use of the science or art of interpretation. The basic concept governing the applicability of this technique and the steps necessary to ensure the development of the full potential of aerial photography in its application, are discussed and illustrated by detailed accounts of a number of specific projects. These projects incorporate both materials appraisals of wide strips of country for route location purposes and intensive prospecting along chosen routes. The techniques thus developed, constitute a new approach to materials investigations for major road projects and in this respect contribute to knowledge in this field. Finally, conclusions are drawn on the relative merits of materials investigation methods in current use in South West Africa and on how these methods affect the different organisations involved in the planning and construction of major road projects. The use made of airphoto interpretation for similar engineering works in other countries, as well as the possible future scope for the application of the particular method of materials investigation described in this thesis, are also covered.