[QGIS-Developer] QGIS Server request extra parameters as variables for expressions

[Matthias Kuhn]

On 11/24/2017 11:02 AM, René-Luc Dhont wrote:
> @Arnaud:
>
> There is no WMS dimensions in QGIS server roadmap
>
> @Richard:
>
> Which one of the three GeoServer implementation is the more 'common'
> way ?
>
>
> To my point of view, having the capability to update QGIS Variables
> through HTTP parameters will be a great enhancement.

For the configuration part, it would be best to explicitly list
variables that are meant to be modified in the server options. Basically
adding a new Server scope to the expressions which is applied after
global and project scope. The interface would be the same table the one
already available for global, project, layer... scope, just in the OWS tab.

This should then be available to filter, style, or otherwise prepare
raster, vector or other data without further ado.

How this is then exposed to webservices is a different question, to
which I agree that it would be best to build it on top of existing
protocols (dimensions or whatever else is around).

Best regards
Matthias

>
> About the WMS dimensions, QGIS will need some enhancement about Raster
> data to apply filtering, changes band in style and/or use expression
> for styles.
>
> Regards,
>
> René-Luc
>
>
> Le 23/11/2017 à 20:53, Richard Duivenvoorde a écrit :
>> On 23-11-17 16:46, Arnaud Morvan wrote:
>>
>>> @Mathias :
>>>
>>> Yes after taking a look, WMS dimensions is exactly the idea I have
>>> in mind.
>> Mmm,
>>
>> I think Dimensions is a different case, as Dimensions are tied to WMS-T
>> [0] and the query parameter is defined as
>> &TIME=...,...
>> &TIME=...
>> etc
>> OR elevation:
>> &ELEVATION=
>>
>> GeoServer has (besides dimensions) even some more use of 'variables'
>> which you can use in different places:
>>
>> - possible variable substitutions in sld's [1]
>> &&env=name1:value1;name2=value2&...
>>
>> - sql view parameters [2]
>> &viewparams=p1:v1;p2:v2;...
>>
>> - format options in CQL queries [3]
>> &format_options=param1:value1;param2:value2;...
>>
>> I think the 'expressions'-variables you are talking about are most close
>> to the viewparams (though if it only filters the styling itis a sld
>> one...).
>>
>> My point: let's define a 'common' param, shared between different FOSS
>> wms's instead of coming up with our own wheel :-)
>>
>> Regards,
>>
>> Richard Duivenvoorde
>>
>> [0]
>> https://anitagraser.com/2011/06/10/wms-t-support-in-geoserver-and-mapserver/
>>
>> [1]
>> http://docs.geoserver.org/stable/en/user/styling/sld/extensions/substitution.html
>>
>> [2] http://docs.geoserver.org/latest/en/user/data/database/sqlview.html
>> [3] http://docs.geoserver.org/latest/en/user/services/wfs/vendor.html
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