Hi,
In QGIS there is something what we call 'Geometry-generators': you actually generate a geometry based on some other geometry and some parameters, coming from 'expressions'.
In this way it is for example possible to create some kind of polygon based on a point layer.
My goal: create rotated 'wedges/sectors' with a data-based rotation from a point layer (talking about GSM 'beams' here), but (tricky part): size depending on the current map scale...
My plan to mimic this in a Geoserver WMS:
- have a point layer in postgis
- create a postgis function to create a wedge (taking the attribute in account)
- create a SQL view layer which creates a geom by calling this function
Question: is it possible for geoserver to 'insert' the scale (as being requested in the WMS request) into this function-call as parameter. Something like $SCALE or $SCALE_DENOMINATOR or so, which is to be replaced by Geoserver BEFORE handling over the query to postgis?
Looking into the docs[0], it looks like it would be possible with a (client site added) parameter. But in this case the 'scale'-information should come from the WMS-request-info (as it is not possible to change the client apps for us).
Mmm, now I am afraid this is maybe hard as it makes it impossible to 'cache' this view...
Anyone idea's?
Regards,
Richard Duivenvoorde
[0] https://docs.geoserver.org/stable/en/user/data/database/sqlview.html
It might be easier to do this in a custom function in GeoTools rather than in PostGIS - then you could pass in the scale env variable along with the feature that you are drawing.
Ian
···
Ian Turton
On 8/3/20 12:40 PM, Ian Turton wrote:
It might be easier to do this in a custom function in GeoTools rather than in PostGIS - then you could pass in the scale env variable along with the feature that you are drawing.
Ian
Mmm, that is (at least in my opinion) a little over the top... Adding java functions does not count as configuration I think 
I was hoping that I could use some kind of variable for this. Like you can apparently use 'wms_scale_denominator' in sld symbolizers:
https://docs.geoserver.org/stable/en/user/styling/sld/extensions/substitution.html
As an work-around in this case I can off course add the rules for every zoom level...
Regards,
Richard Duivenvoorde
wms_scale_denominator is a “env” variable that only the “env” function sees,
while view params follow a completely different path.
It would be possible to load up all env variables into the view params map I guess,
I assume it would have to be done with a new config flag to avoid potential regressions for
existing installations… and it would require some java coding, too 
Cheers
Andrea
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Regards, Andrea Aime
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