Layer get distinct function...

[Frank Warmerdam]

Yewondwossen Assefa wrote:
> It can be costly in some cases but I can also see the immediate use for
> me in the time support where the user sends a request like Time=current
> (or Time=now).
>
>
> Steve Lime wrote:
>
>> Hi all: Tom's recent post about time and WMS reminded me of a feature
>> that might be useful for WCS/WMS and other interfaces. The ability to
>> get a list of distinct values for an attribute within a layer. At the
>> moment with WCS for example you have to explicitly enter all available
>> times in metadata. Works fine for a few but would get tedious quickly. I
>> could also see this as being a way to extend templates to be more
>> dynamic (e.g. produce a select list) and data driven. It would be very
>> helpful to be able to mine the data for that list. I'd like to propose a
>> msLayerGetDistinct function that would return an array of all unique
>> values for an attribute. What do folks think, other better ideas?

Steve,

I am also ok with adding the distinct capability though it will be pretty
expensive to execute for most OGR drivers.  I gather folks can still
declare the list of values in the metadata to avoid this cost, right?

What about providers that might not get updated to support this capability.
What will happen then?

Best regards,
--
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I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam at pobox.com
light and sound - activate the windows | http://pobox.com/~warmerdam
and watch the world go round - Rush    | Geospatial Programmer for Rent