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Hi Bruce, on conceptual level, I fully agree that the question of merging both types is extremely interesting. I find questioning the boundaries between both very appropriate, in particular when it comes to generalizations of raster grids. It should be really interesting to come up with a unified model.
From a practical viewpoint, however, all methodologies and tools
distinguish between vector and raster data. Not only in terms of data structures, but also in terms of operations (how would all that image processing fit into a feature world...). And IMHO standards should not (or perhaps not always) redefine the world, but provide a platform where tool vendors and users find themselves understood to the largest possible extent. Hence, for the moment being it seems like we have to stick with feature/coverage types. (Hm, rereading this it might seem a little harsh in phrasing. Sorry if it appears so, it wasn't meant like that. But too close to midnight to start over now.) cheers, Peter Wright, Bruce wrote:
[...] 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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