[QGIS-Developer] ArcGIS Feature Server Advanced Symbology Parsing

[Dror Bogin]

Hi everyone,

I found a URL parameter that can be added to ArcGIS FeatureServer service
layers that makes the server return more complete and advanced rendering
instructions for the layers.

The difference is mostly seen in layers which use multiple symbol layers
such as polygons with a hatch fill. For layers like that, ArcGIS servers
usually return a single symbol with the colors mixed.
I recommend trying to load the example below, first as a mapserver service
to see the definitions and then as a featureserver service to see how the
drawing info is currently being passed.

I found that if you query the layer metadata with the
*returnAdvancedSymbols* URL parameter set to true, you get back the same
response that ArcGIS Pro gets from the server and uses to create symbology
for feature services.

So instead of requesting the metadata for a layer like QGIS currently does:
https://ags.iplan.gov.il/arcgisiplan/rest/services/PlanningPublic/Xplan/MapServer/4?f=json

The initial metadata query would be:
https://ags.iplan.gov.il/arcgisiplan/rest/services/PlanningPublic/Xplan/MapServer/4?f=json&returnAdvancedSymbols=true

And get back a more complex result if there are advanced symbols on the
layer. The drawingInfo returned is *mostly* compatible with the ESRI CIM
spec, <https://github.com/Esri/cim-spec> but I already encountered some
names that differed between server versions.
While the parameter only appears in esri documentation from version 11.1, I
tested that it is working for services running on ArcGIS Server version as
far back as at least 10.6.

I tried to start implementing this parsing in QGIS (image 3 shows rendering
with my additions), but I want to make it optional until the parsing is
complete and that is where I could use some help.
I added a checkbox to *QgsNewArcGisRestConnectionDialog* where the user can
toggle advanced symbols for a specific service, and managed to save the
setting in the service settings in the profile's QGIS3.ini file.

What I want to do next is pass this parameter on to *QgsAfsProvider* where
I would use that as a switch between *QgsArcGisRestQueryUtils::getLayerInfo*
and the function I added to get the metadata with advanced symbols called
*QgsArcGisRestQueryUtils::getLayerAdvanvcedSymbolsInfo*.

I could use some help in understanding how to read and pass on the
parameter through the QgsAfsSharedData object or in any other way that
might be more correct.

On a side note, I am in the contributor meeting right now until lunch in
case someone is here and can help with this face to face, it would be much
appreciated.

On a second side note, sample service with other types of complex symbols
for points, lines and polygons will also be much appreciated for testing
purposes.


-- 
Regards,

Dror Bogin, +972-50-3077338
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