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Hi Peter, You wrote:
...and then you are right in that the terms coverage and feature are not really clearly distinct in their meaning. Up to now we occasionally heard voices stating that "coverages are features". Now, true, but what does this help us in practice? Some people start encoding coverages in GML which I find not the best of all possible ideas when it comes to a generic (n-D) solution. Now you are AFAIK the first one to state that the inverse holds as well: "features are coverages, sort of". A remarkable point in history! ;-) Seriously, I believe that when it comes to border cases there is a degree of freedom to the data designer, which is not bad. So I feel that WFS and WCS nicely coexist, augmented by the third companion, metadata served by a CS-W.
I think this 'features vs. coverages' (or WFS vs. WCS) is an interesting issue; I've seen a number of different, but not necessarily exclusive, viewpoints: 1. Coverages and features are different...WFS and WCS evolved as two distinct services to meet different requirements for accessing data and metadata. 2. A coverage is a feature...features and coverages are different 'cross-sections' through the information - Simon Cox presents this nicely by considering the information as tabular, with a row represents a feature (a series of individual property values) and a column representing a coverage (different values of the same property) - and the WFS and WCS should be harmonised. 3. A feature is a coverage...coverages are already effectively being encoded in GML for some WFS requests that need to return the variation of a set of parameters over space/time (normally small data volumes); again, this suggests that the WFS and WCS should be harmonised. 4. Coverage is a property of a feature... WCS is a convenience interface, which should eventually replaced by an enhanced WFS, which adds a GetCoverage request (or an OPeNDAP request!) Personally, I think these are all true to some extent (not sure 3. above is a good thing though!). However, which viewpoint you take determines how you develop and implement these web services going forward (e.g. my explicit 'conclusion' on 4. above!). Regards, Bruce
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