Re: [galeon] WCS core + extensions

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Ethan-
resonses inline:

Ethan Davis wrote:

Hi Peter,

So the extensions are global (GetCapabilities) but may affect some of
the options available at the coverage level (DescribeCoverage)?


not quite: the global extensions affect the possible values of
parameters. For example, the format extensions picked by the server
implementor determine which names can be listed in the (always present)
format parameter.



For example: 1) supported encoding format extensions imply which
options will be available in the supported formats section of the
DescribeCoverage; 

yes


2) any extension that spells out the type(s) of CRS supported imply
the structure/dimensionality/etc of the CRS in DescribeCoverage; 

our intention is the inverse: the structure/dimensionality will
implicitly (or explicitly? we'll have to see) determine which CRSs make
sense.


and 3) any extension that describes a new type of interpolation imply
the options available in the interpolation section of the
DescribeCoverage.


interpolation types are fixed in ISO 19123, thus not likely to change.
Any homegrown method - as of today - would go under "other". But still,
introducing a new interpolation method simply would add one possible
value for the resp. parameter.



Is it the extensions job to describe if and how it affects the
DescribeCoverage? Or does the WCS specification spell out certain
locations in the DescribeCoverage that extensions can affect?


Extensions determine which parameter combinations are allowed.
Additionally, extensions may introduce new parameters (although we try
to limit this as much as possible).
Finally, an extension can introduce a new request type. WCS-T adds the
upload facility, WCPS adds the ProcessCoverages request type.

However, I personally believe that an extension cannot redefine existing
parameters in some surprising manner.

That said I am still awaiting the final verdict of the Architecture WG
on the details of the extension mechanics, although we have done the
first two extensions already and are on our way for further ones.
Parallel processing, ya know ;-)

-Peter
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