Fast approximation of visibility dominance using topographic features as targets and the associated uncertainty

An approach to reduce visibility index computation time andmeasure the associated uncertainty in terrain visibility analysesis presented. It is demonstrated that the visibility indexcomputation time in mountainous terrain can be reduced substantially,without any significant information loss, if the lineof sight from each observer on the terrain is drawn only to thefundamental topographic features, i.e., peaks, pits, passes,ridges, and channels. However, the selected sampling of targetsresults in an underestimation of the visibility index ofeach observer. Two simple methods based on iterative comparisonsbetween the real visibility indices and the estimatedvisibility indices have been proposed for a preliminary assessmentof this uncertainty. The method has been demonstratedfor gridded digital elevation models

Grid models versus TIN : geometric accuracy of multibeam data processing

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Exploring multiple viewshed analysis using terrain features and optimisation techniques

The calculation of viewsheds is a routine operation in geographic information systems and is used in a wide range of applications. Many of these involve the siting of features, such as radio masts, which are part of a network and yet the selection of sites is normally done separately for each feature. The selection of a series of locations which collectively maximise the visual coverage of an area is a combinatorial problem and as such cannot be directly solved except for trivial cases. In this paper, two strategies for tackling this problem are explored. The first is to restrict the search to key topographic points in the landscape such as peaks, pits and passes. The second is to use heuristics which have been applied to other maximal coverage spatial problems such as location-allocation. The results show that the use of these two strategies results in a reduction of the computing time necessary by two orders of magnitude, but at the cost of a loss of 10% in the area viewed. Three different heuristics were used, of which Simulated Annealing produced the best results. However the improvement over a much simpler fast-descent swap heuristic was very slight, but at the cost of greatly increased running times. © 2004 Elsevier Ltd. All rights reserved

Enhancement of height system for Malaysia using space technology: the study of the datum bias inconsistencies in Peninsular Malaysia

The algorithm for orthometric height transfer using GPS has been widely presented. Its practical limitations are mostly due to datum bias inconsistencies and lack of precise geoid. In most applications, datum biases are assumed to be systematic over short baselines and therefore could be eliminated by differential heighting techniques. In this study, optimal algorithms were investigated to model biases between local vertical datum in Peninsular Malaysia and the datums implied by by EGM96, OSU91A and the regional Gravimetric Geoid in South_East Asia. The study has indicated that local vertical datum is not physically parallel to the datums implied by the above geoids. The shift parameters between the datums implied by the GPS/leveling data, and the EGM96, OSU91A and the gravimetric datums are about – 41cm, -54 cm and – 8 cm respectively. Also the maximum tilts of the planes fitting the residual geoids above these datums relative to GPS/Leveling datum are of the order of 36, 51 and 33 centimeters per degree. It is therefore necessary to take into account the effect of inconsistent datum bias particularly for baseline height transfer. The level of accuracy achieved by the bias corrected relative orthometric height differences of the EGM96, OSU91A and the gravimetric geoid models combined with GPS/leveling data for baseline lengths up to 36 km, is sufficient to replace the conventional tedious, time consuming ordinary leveling technique for rapid height transfer for land surveying and engineering applications

Remote sensing applications in forestry - The development of an earth resources information system using aerial photographs and digital computers Annual progress report

Earth resources information system using aerial photographs and digital computer