Dear list, Sorry for the delay in sending a summary, just got back to work.
In a previous mail I was asking about the need for more advanced algorithms in the case one has well structured monitoring networks. While looking at decision support systems used for radiological monitoring, I noticed that TINs are used rather than sophisticated algorithms and estimation uncertainties do not seem to be taken into account. Reasonably in terms of minimizing health risks, efforts are focusing on increasing the density of the monitoring network rather than on improving mapping algorithms. With no surprise, linear interpolators (i.e. TIN) are thus used to draw radiological maps on an automatic basis as TIN will show exact levels at the monitoring stations and outliers are thus so immediately highlighted. In the replies I got, Andrew Hunter underlined a number of advantages of TIN: it minimizes data storage requirements by allowing the density of triangles to vary over the surface to reflect its variability. The data structure further allows surface derivatives such as slope and aspect, or surface normal information to be calculated and stored for each triangle, edge or node, thereby improving performance of subsequent surface analysis. However, it requires that samples are located appropriately - peaks and troughs are sampled at an appropriate interval, and triangle edges are forced to follow breaklines within the surface. Drawbacks are that discontinuities across triangle or grid edges will occur when using most linear interpolation techniques. Also, most exact interpolators have zero degrees of freedom (dof); hence, estimates of uncertainty are not possible. Maurizio Trevisani further commented on the need to detect "outliers" which can be enhanced by time series. Sebastiano Trevisani commented on the use of linear interpolators, mentioning the use of Natural Neighbours, wondering about the relative advantages and drawbacks of the method when compared with TIN. Thanks to all for the feedback. Best wishes, Gregoire __________________________________________ Gregoire Dubois (Ph.D.) JRC - European Commission IES - Emissions and Health Unit Radioactivity Environmental Monitoring group TP 441, Via Fermi 1 21020 Ispra (VA) ITALY Tel. +39 (0)332 78 6360 Fax. +39 (0)332 78 5466 Email: [EMAIL PROTECTED] WWW: http://www.ai-geostats.org WWW: http://rem.jrc.cec.eu.int "The views expressed are purely those of the writer and may not in any circumstances be regarded as stating an official position of the European Commission."
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