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For the WCS not to disallow N-D access in the core, all of the operators/functions/concepts for operating on N-D data (such as time, altitude, and all other non-horizontal spatial coordinates/operators/filters) must be listed but not be required. The mechanisms need to be there even though they are not required, or there is no standardized way to access N-D data through the core specification alone. Is a client who does not understand a particular CRS offered by a WCS implementation non-compliant? For example, my WCS client knows how to read data in a Lambert Conformal Conic projections, but not in EPSG 2017. My understanding is that CRS's are required to be "well-known", not that they be in a limited set that all client and server implementations understand. I see this as a similar case, because just as a client can decide whether or not it knows how to deal with a particular CRS, it can also decide whether it is capable of dealing with any particular dimensionality of data. Both seem like discoverable aspects of the native dataset. Aaron Wenli Yang wrote:
I might be wrong about why the core vs extension design was introduced. But I guess that the reason to have a "core" was to set a MINIMUM requirement for a WCS server to be considered compliant. Anything in "core" means mandatory. Thus,the reason that ONLY 2-D, but not a more general n-D, is mandatory was to make it easier for servers/clients to be considered "compliant". If the core requires n-D, with n being > 2 included, then a 2-D client is considered "NOT compliant" when it fails to understand a 4-D server's offering of subsetting along some non-spatial dimensions/axes. On the other hand, I would like to see n-D data to be included in WCS. Most of the data sets I have used are 3D data arrays (two spatial D plus a parameter D) and some are 4D (two spatial plus one time plus a parameter dimensions). I perhaps feel more comfortable of seeing my data as just an n-D data array without having to tell domain dimensions from range axes. -- Wenli
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