# A survey system for dredging

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## Abstract

A survey system for dredging1 Brouns G . and A. De W u lf Ghent University, Department o f Geography/Surveying Krijgslaan 281 - S8 B-9000 Gent E-mail: [email protected] In bathymetry, the seafloor's depth is sounded at discrete spots. For dredging works, it is important to have as good a terrain model as possible, as well before dredging starts as after the work has been carried out. The latest bathymetric sounding equipment that is available nowadays, especially the multibeam echosounder, yield a very dense bottom sampling. When compared to the common singlebeam echosounder, an enormous amount of data is produced that needs to be processed in a correct and fast way. Grid-overlay (linear interpolation by means of a regular mesh) is not an option here as this method yields an interpolation of the measured values and hence will either cause accuracy loss or generate a still larger amount of data. A triangular irregular network (TIN fo r short), especially the Delaunay triangulation (Dt), does respect the actual measurements and will not generate new data. In literature, a number of algorithms have been developed that determine the Dt o f a set of points given in the plane. The speed of an algorithm is expressed as a function of n, the number o f points to be processed. A straightforward algorithm to obtain a Dt is adding the points one by one to an initial triangulation made of a subset of the data. This method requires n2 manipulations. However, algorithms exist, under which a divide-and-conquer algorithm, that require only n.log(n) manipulations. That has been proved to be theoretically the best possible performance. This means a considerable gain in calculation time of the concerned data files, which typically will contain about 1 O6 points. It will be clear that the processing time for both algorithms will even more diverge for increasing data sets. Therefore, the first and most important part of the project consists of optimally implementing the divide- and-

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