[Qgis-user] Programmatically extract WMS data based on point layer?

Mon Oct 19 06:17:59 PDT 2020

Just checking :-)
https://www.lfu.bayern.de/gdi/wfs/natur/oefk

which returns:
Error occurred while processing request
Type: Status Report
Message:
Description: http.400:
*ArcGIS Server*

So apperently ArcGIS Server, no wonder they have to ask money for everything, they need the money for all the licenses ;-)

I thought you wanted to create some PyQGIS script for it.
The reason this seems not to work (yet), is that QGIS is a c++ program with python bindings for almost everything, but not everything.
I think devs could make my example work, but there was no use case for it yet...

But... if your are not into Python, what would be your preferred scripting language be then?

Given a WMS getMap request like:
https://www.lfu.bayern.de/gdi/wms/natur/oefk?SERVICE=WMS&VERSION=1.3.0&REQUEST=GetMap&BBOX=5330491.995354886167,3656773.878684170544,5332123.064803482033,3661911.927476988174&CRS=EPSG:31467&WIDTH=1428&HEIGHT=453&LAYERS=oekoflaechen&STYLES=&FORMAT=image/jpeg&DPI=96&MAP_RESOLUTION=96&FORMAT_OPTIONS=dpi:96

You would end up to create GetFeatureInfo requests like this to return in html:
https://www.lfu.bayern.de/gdi/wms/natur/oefk?SERVICE=WMS&VERSION=1.3.0&REQUEST=GetFeatureInfo&BBOX=5330491.99535488616675138,3656773.87868417054414749,5332123.06480348203331232,3661911.92747698817402124&CRS=EPSG:31467&WIDTH=1427&HEIGHT=453&LAYERS=oekoflaechen&STYLES=&FORMAT=image/jpeg&QUERY_LAYERS=oekoflaechen&INFO_FORMAT=text/html&I=544&J=361&FEATURE_COUNT=10

Or in plain/text (VERY ugly formatted!):
https://www.lfu.bayern.de/gdi/wms/natur/oefk?SERVICE=WMS&VERSION=1.3.0&REQUEST=GetFeatureInfo&BBOX=5330491.99535488616675138,3656773.87868417054414749,5332123.06480348203331232,3661911.92747698817402124&CRS=EPSG:31467&WIDTH=1427&HEIGHT=453&LAYERS=oekoflaechen&STYLES=&FORMAT=image/jpeg&QUERY_LAYERS=oekoflaechen&INFO_FORMAT=text/plain&I=544&J=361&FEATURE_COUNT=10

So theoretically you could create some script to just fire the GetFeatureInfo-requests. Main drawback is for a request to be valid, your bbox and width/height should be in par with your x,y (mmm, ArcGis apparently uses I J, which are pixels! in the bbox/width/height)... So I think that is pretty difficult.

So my conclusion, not as easy as you hoped I think, best would be to just get the data from somewhere, not sure if hacking your code will be easier...
but it 
- would be 'easiest' in PyQGIS (because the 'indentify' is easier to script, because you can use QGIS magic to determine bbox/width and height params)
- or recreate valid getfeatureinforequests and fire those in some other  script language

Looking that the result in QGIS, there is not so much info in it, just 4 fields.... one of them the area.

Regards,

Richard Duivenvoorde

On 10/19/20 2:45 PM, Bernd Vogelgesang wrote:
> Hi Richard,
> 
> your last question first: Nope, there is definitely no WFS (would be too easy). I am living in Bavaria, the home of "Laptop and Lederhosen". Our administrations are among the greediest and most retarded (offering hardly any WFS which then mostly have to paid as well) in Germany.
> 
> How would I know this is a Geoserver instance? The url of the WMS is |https://www.lfu.bayern.de/gdi/wms/natur/oefk?|
> 
> My "python" is actually nonexistant, so I was hoping that there was something "prebuilt" in someone's drawer already. But as my web research showed, there does seem to be much on this topic besides of "not possible".
> 
> It's a bit mystical to me why QGIS can show the result of a click on a layer, but not store the data by any means ...
> 
> Mhm ...
> 
> Bernd
> 
> On 19.10.20 14:07, Richard Duivenvoorde wrote:
>> Hi Jorge, Bernd,
>>
>> I thought to play with that, but ...
>>
>> although I get a valid result, I cannot get to the actual features in python:
>>
>> TypeError: unable to convert a C++ 'QgsFeatureStoreList' instance to a Python object
>>
>> So I'm not sure if you could (currently) easily come to the actual feature...
>>
>>
>> What I did (working with a national buildings WMS, and a (to me) known valid x,y,width/height etc:
>>
>> l=qgis.utils.iface.addRasterLayer(
>> "crs=EPSG:28992&layers=Bebouwingvlak&styles=&format=image/png&url=https://geodata.nationaalgeoregister.nl/kadastralekaart/wms/v4_0?", # uri
>> "buildings", # name for layer (as seen in QGIS)
>> "wms" # dataprovider key
>> )
>>
>> result = l.dataProvider().identify( QgsPointXY(104606,490213),
>>              QgsRaster.IdentifyFormatFeature,
>>              QgsRectangle(104391.1406077263819,490161.0749502293766,104899.6563292678911,490283.3410253541078),
>>              1465,
>>              352,
>>              96)
>> print(result.isValid()) # prints True
>> print(result.results())
>> # prints TypeError: unable to convert a C++ 'QgsFeatureStoreList' instance to a Python object
>>
>> Regards,
>>
>> Richard Duivenvoorde
>>
>> PS @Bernd: you are sure there is no WFS running there (if it is a Geoserver instance, it often has (silently) also a WFS....)?
>>
>> On 10/19/20 1:36 PM, Jorge Gustavo Rocha wrote:
>>> Hi Bernd,
>>>
>>> Try rlayer.dataProvider().identify()
>>>
>>> Checks the docs at https://docs.qgis.org/3.10/en/docs/pyqgis_developer_cookbook/raster.html#query-values
>>>
>>> Good luck,
>>>
>>> Jorge
>>>
>>> Às 12:25 de 19/10/20, Bernd Vogelgesang escreveu:
>>>> Hi there,
>>>>
>>>> unfortunately I am provided with data only in form of a WMS layer
>>>> representing areas as polygons.
>>>> These areas match with the cadastral boundaries.
>>>> I am looking for a way how to hand over the data from the WMS to my
>>>> cadastral units to be able to really work with these informations.
>>>>
>>>> I created a "Point on surface" layer of the cadastre.
>>>> Is there any pythonic or other way to "mimic" the "Identify features"
>>>> click on that layer with the coordinates of those points and store the
>>>> results?
>>>>
>>>> I assume, that each click is a server request, so running these (in my
>>>> case) 8000 "cĺicks" should not be sent in a millisecond, but with some
>>>> pause.
>>>> It doesn't really matter how long this takes, cause it only has to be
>>>> done once and would be in any case faster than manually clicking and
>>>> noting the data.
>>>>
>>>> Obviously, this is not what the provider of the data intends, but it's
>>>> like an act of self-defence against a stubborn and bureaucratic
>>>> administration.
>>>> So, data rebels, come to help please ;)
>>>>
>>>> Cheers,
>>>>
>>>> Bernd
>>>>
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