[QGIS-Developer] QGIS-Server: filter by categories in an OGC compatible way

Tue Apr 9 10:09:27 PDT 2019

Hi Andreas,

Another problem you may hit - the link below is hitting it being ~2300 
chars - URL's (and thus GET requests) cannot reliably be more than about 
2000 characters long. At that point you need to shift over to POST 
requests (and I think GetMap is GET only...).

https://stackoverflow.com/questions/417142/what-is-the-maximum-length-of-a-url-in-different-browsers

Cheers,

Jonathan

On 2019-04-09 16:07, Andreas Neumann wrote:
> Hi Paul
> Thanks - now I know that I have to use SLD_BODY for the case where the
> SLD is in the URL.
> Another QGIS-Server specific question:
> Can I count on it that the SLD output by QGIS server with the GetStyles
> request can also be consumed again by QGIS server? What about complex
> styles (e.g. something with a style that can't easily be represented by
> SLD). If I first consume the styles from QGIS server, then filter and
> send back, would the complex styles potentially be lost/destroyed?
> Again: our intent here is merely to filter categories, not to change the
> styles.
> Thanks,
> Andreas
> On 2019-04-09 16:28, pblottiere wrote:
>
>> Hi Andreas,
>>> Can you point me to an example how to create a valid GetMap request 
>>> with an SLD submitted? 
>>
>> There's a basic example in unit tests: 
>> https://github.com/qgis/QGIS/blob/master/tests/src/python/test_qgsserver_wms_getmap.py#L1309-L1325
>>
>> Regards,
>>
>> Paul
>> On 4/9/19 4:14 PM, Andreas Neumann wrote:
>> Hi,
>> I did some test:
>> Here is a long URL with the SLD (originally sent by QGIS server, 
>> stripped away some RULES manually) and sending it back in a GetMap 
>> request:
>>
> https://services.geo.zg.ch/ows-oereb/Grundwasserschutz?SERVICE=WMS&VERSION=1.3.0&REQUEST=GetMap&BBOX=2682932,1225299,2684213,1226054&CRS=EPSG:2056&WIDTH=1615&HEIGHT=952&LAYERS=ch.zg.grundwasserschutz.gwszonen&STYLES=&FORMAT=image/png&DPI=96&MAP_RESOLUTION=96&FORMAT_OPTIONS=dpi:96&TRANSPARENT=TRUE&SLD=%3CStyledLayerDescriptor+xmlns%3D%22http%3A%2F%2Fwww.opengis.net%2Fsld%22+xmlns%3Axlink%3D%22http%3A%2F%2Fwww.w3.org%2F1999%2Fxlink%22+xmlns%3Axsi%3D%22http%3A%2F%2Fwww.w3.org%2F2001%2FXMLSchema-instance%22+xsi%3AschemaLocation%3D%22http%3A%2F%2Fwww.opengis.net%2Fsld+http%3A%2F%2Fschemas.opengis.net%2Fsld%2F1.1.0%2FStyledLayerDescriptor.xsd%22+xmlns%3Ase%3D%22http%3A%2F%2Fwww.opengis.net%2Fse%22+version%3D%221.1.0%22+xmlns%3Aogc%3D%22http%3A%2F%2Fwww.opengis.net%2Fogc%22%3E%0D%0A+%3CNamedLayer%3E%0D%0A++%3Cse%3AName%3Ech.zg.grundwasserschutz.gwszonen%3C%2Fse%3AName%3E%0D%0A++%3CUserStyle%3E%0D%0A+++%3Cse%3AName%3Edefault%3C%2Fse%3AName%3E%0D%0A+++%3Cse%3AFeatureTypeStyle%3E%0D%0A++++%3Cs 
>
> e%3ARule%3E%0D%0A+++++%3Cse%3AName%3EGrundwasserschutzzone+S1%3C%2Fse%3AName%3E%0D%0A+++++%3Cse%3ADescription%3E%0D%0A++++++%3Cse%3ATitle%3EGrundwasserschutzzone+S1%3C%2Fse%3ATitle%3E%0D%0A+++++%3C%2Fse%3ADescription%3E%0D%0A+++++%3Cogc%3AFilter+xmlns%3Aogc%3D%22http%3A%2F%2Fwww.opengis.net%2Fogc%22%3E%0D%0A++++++%3Cogc%3APropertyIsEqualTo%3E%0D%0A+++++++%3Cogc%3APropertyName%3Etyp_code%3C%2Fogc%3APropertyName%3E%0D%0A+++++++%3Cogc%3ALiteral%3ES1%3C%2Fogc%3ALiteral%3E%0D%0A++++++%3C%2Fogc%3APropertyIsEqualTo%3E%0D%0A+++++%3C%2Fogc%3AFilter%3E%0D%0A+++++%3Cse%3APolygonSymbolizer%3E%0D%0A++++++%3Cse%3AFill%3E%0D%0A+++++++%3Cse%3ASvgParameter+name%3D%22fill%22%3E%23003bb3%3C%2Fse%3ASvgParameter%3E%0D%0A++++++%3C%2Fse%3AFill%3E%0D%0A++++++%3Cse%3AStroke%3E%0D%0A+++++++%3Cse%3ASvgParameter+name%3D%22stroke%22%3E%23000080%3C%2Fse%3ASvgParameter%3E%0D%0A+++++++%3Cse%3ASvgParameter+name%3D%22stroke-width%22%3E1%3C%2Fse%3ASvgParameter%3E%0D%0A+++++++%3Cse%3ASvgParameter+name%3D%22stroke-linej 
>
> oin%22%3Ebevel%3C%2Fse%3ASvgParameter%3E%0D%0A++++++%3C%2Fse%3AStroke%3E%0D%0A+++++%3C%2Fse%3APolygonSymbolizer%3E%0D%0A++++%3C%2Fse%3ARule%3E%0D%0A+++%3C%2Fse%3AFeatureTypeStyle%3E%0D%0A++%3C%2FUserStyle%3E%0D%0A+%3C%2FNamedLayer%3E%0D%0A%3C%2FStyledLayerDescriptor%3E 
>
>>
>> The response is:
>>
>> <ServiceExceptionReport xmlns="http://www.opengis.net/ogc" 
>> version="1.3.0">
>> <ServiceException code="Invalid Parameter"> SLD 
>> ('<StyledLayerDescriptor xmlns="http://www.opengis.net/sld" [1] 
>> xmlns:xlink="http://www.w3.org/1999/xlink" [2] 
>> xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" [3] 
>> xsi:schemaLocation="http://www.opengis.net/sld 
>> http://schemas.opengis.net/sld/1.1.0/StyledLayerDescriptor.xsd" [4] 
>> xmlns:se="http://www.opengis.net/se" [5] version="1.1.0" 
>> xmlns:ogc="http://www.opengis.net/ogc" [6]> <NamedLayer> 
>> <se:Name>ch.zg.grundwasserschutz.gwszonen</se:Name> <UserStyle> 
>> <se:Name>default</se:Name> <se:FeatureTypeStyle> <se:Rule> 
>> <se:Name>Grundwasserschutzzone S1</se:Name> <se:Description> 
>> <se:Title>Grundwasserschutzzone S1</se:Title> </se:Description> 
>> <ogc:Filter xmlns:ogc="http://www.opengis.net/ogc" [6]> 
>> <ogc:PropertyIsEqualTo> <ogc:PropertyName>typ_code</ogc:PropertyName> 
>> <ogc:Literal>S1</ogc:Literal> </ogc:PropertyIsEqualTo> </ogc:Filter> 
>> <se:PolygonSymbolizer> <se:Fill> <se:SvgParameter 
>> name="fill">#003bb3</se:SvgParameter> </se:Fill> <se:Stroke> 
>> <se:SvgParameter
> name="stroke">#000080</se:SvgParameter> <se:SvgParameter 
> name="stroke-width">1</se:SvgParameter> <se:SvgParameter 
> name="stroke-linejoin">bevel</se:SvgParameter> </se:Stroke> 
> </se:PolygonSymbolizer> </se:Rule> </se:FeatureTypeStyle> </UserStyle> 
> </NamedLayer> </StyledLayerDescriptor>') cannot be converted into QString
>> </ServiceException> </ServiceExceptionReport>
>> So apparently the SLD cannot be converted to a QString. Is my 
>> encoding in the URL above wrong or am I missing a required additional 
>> parameter?
>> Can you point me to an example how to create a valid GetMap request 
>> with an SLD submitted?
>> Thanks a lot, Andreas
>> On 2019-04-09 15:38, Andreas Neumann wrote:
>> Hi,
>> Does QGIS-Server support SLD styles to filter away RULEs in a GetMap 
>> Request?
>> I would assume, yes, but in what encoding would I submit such an SLD 
>> in a GET request? I know that one should rather use POST reqests for 
>> such long parameters, but for experimenting, it would be ok to use GET.
>> The idea would be to allow users to enable/disable categories within 
>> a given layer.
>> The WMS client would first request the available rules with a 
>> GetStyles command (that part works fine) and would then filter the 
>> RULE (strip away the unwanted RULEs) and resubmit the GetMap with an 
>> SLD. Does that work with QGIS server?
>> I know that one can also use the FILTER parameter, but we want to do 
>> it in an OGC compatible way, since the client being developed should 
>> work with any OGC compatible WMS server.
>> Thanks for your reply,
>> Andreas _______________________________________________
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>
> Links:
> ------
> [1] http://www.opengis.net/sld
> [2] http://www.w3.org/1999/xlink
> [3] http://www.w3.org/2001/XMLSchema-instance
> [4]
> http://www.opengis.net/sldhttp://schemas.opengis.net/sld/1.1.0/StyledLayerDescriptor.xsd 
>
> [5] http://www.opengis.net/se
> [6] http://www.opengis.net/ogc
>
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