Hi Michael, Thanks very much for this.
> My naive 2p / 2c worth is that the domain of a coverage is simply that > region within which data are defined. I like this definition because I understand it! However, I'm not sure that everyone has the same view. I think the $64000 question is: does the domain for a single coverage have to be contiguous? If so, this would seem to rule out the use of a Coverage for a discretely-sampled domain in which you don't want to apply interpolation of any kind. If domains are allowed to be non-contiguous then this complicates things somewhat but not impossibly so. I think this has revealed a problem with terminology. It seems that GeoAPI/Tools interprets a DiscreteCoverage to be a discretely-*sampled* coverage, which is nevertheless conceptually a contiguous region (with the gaps filled in by nearest-neighbour interpolation). A ContinuousCoverage might also be discretely sampled but the gaps are filled by some other interpolation method. I don't think this is a very obvious use of the terms. By contrast, I believe that the Climate Science Modelling Language (a GML Application Schema) regards a DiscreteCoverage to be non-contiguous, i.e. the domain consists of a number of sub-domains that do not touch or intersect. Andrew Woolf or Dom Lowe would be able to confirm whether my interpretation is correct here. For the record the CSML interpretation is more obvious to me. The GeoAPI/Tools interpretation differentiates on the basis of interpolation method, which I do not find very satisfactory. But I haven't read the ISO specs - I'm hoping that someone else will do that! ;-) Cheers, Jon P.S. I know this conversation has become a bit fragmented. I'll try to find time to type this up on a web page or something. On Fri, Jun 13, 2008 at 9:29 AM, Michael Bedward <[EMAIL PROTECTED]> wrote: > G'day Jon, > > Good questions - I like it when computing, science and epistemology collide :) > > My naive 2p / 2c worth is that the domain of a coverage is simply that > region within which data are defined. i will now try to argue that > that is not a tautology... > > Following on from your example of a set of points, yes - we might > decide to restrict ourselves to the convex hull and call that the > domain, but there are many other possibilities. Based on our > knowledge of the data, prior experience, available literature etc. we > may well feel confident in defining a domain boundary that extends > some way beyond the data points. This may end up being represented > digitally as a coverage within which there is a data domain, possibly > quite complex in shape, with some surrounding NODATA area. Extending > this idea further, we might get trendily Bayesian :) and dispense with > a hard domain boundary altogether, defining instead a gradient of > 'reliability of interpolation' or 'expected predictive accuracy' or > some such term. Then, when we use data directly from this domain, or > aggregate it, or make inferences from it, we will also take into > account the predictive accuracy to put bounds around our results. > > I think there is an argument for not attaching an interpolation method > to a coverage. I'll give a real example here. Decisions about the > conservation status of plant and animal species are frequently made on > the basis of fairly coarse raster data, e.g. national or state-wide > censuses where a data from a wide variety of sources, collected with > different methods and at different scales, have been aggregated into a > relatively small number of grid cells. If part of the decision > process involves determining the area over which a species occurs then > the grid cell size is obviously important. There are examples where > it has been impossible for any species to be rated at the highest > status because there was an area threshold that was smaller than the > grid cell size ! Some researchers have looked at ways of > interpolating within cells in such raster data, based on theoretical > patterns of distribution (e.g. fractal scaling) and/or expert > knowledge of fine scale factors influencing a species' occurrence. > Whether or not you want to do this will depend on (a) the nature of > the exercise (b) the available data and your confidence in the > theoretical underpinnings of the approach (c) convincing the punters > to accept it :) These are case-specific decisions and not something > that is bound up in the coverage itself. > > Jeepers, I've gone on a bit there - sorry. But it's very interesting > stuff and well worth discussing because of all the very practical > implications of alternative approaches. > > cheers > Michael -- -------------------------------------------------------------- Dr Jon Blower Tel: +44 118 378 5213 (direct line) Technical Director Tel: +44 118 378 8741 (ESSC) Reading e-Science Centre Fax: +44 118 378 6413 ESSC Email: [EMAIL PROTECTED] University of Reading 3 Earley Gate Reading RG6 6AL, UK -------------------------------------------------------------- ------------------------------------------------------------------------- Check out the new SourceForge.net Marketplace. It's the best place to buy or sell services for just about anything Open Source. http://sourceforge.net/services/buy/index.php _______________________________________________ Geotools-gt2-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/geotools-gt2-users
