Hi Devs
I am currently working on the "ArcGIS REST API Connector Plugin"[1] trying to
find a way to use QgsVectorLayer. The webservice (callef "ArcGIS Feature
Service") returns valid GeoJSON and the QgsVectorLayer's datasource url can
point to the service that provides this GeoJSON (this is done in the current
version of the plugin). The problem is that there exists no query to retrieve
all features from an ArcGIS Feature Layer at once/in one service call (if there
are more than 1000 features).
So my approach is the following: The feature list is populated through multiple
service calls and temporarily stored/cached as GeoJSON-File. The
QgsVectorLayer's datasource url points to this file. The file is repopulated
occasionally on request/event. Probably the best way to achieve this would be
to write a CustomVectorDataProvider that inherits from VectorDataProvider and
is injected into the VectorLayer. But I didn't find a way to do this with
PyQGIS.
I then tried to use a QgsPluginLayer as an adapter to a QgsVectorLayer. The
CustomPluginLayer would hold a reference to an instance of VectorLayer and
delegates all the functionality of a VectorLayer to this instance. This would
allow the (re)population of the local GeoJSON file, when the layer is loaded or
refreshed. But I didn't find a way to achieve this.
1. What actions are possibly needed to (re)connect?
2. Or are there methods/structures missing in the Python API wrapper to QGIS
C++ API?
3. Is there a good overview/doc over the activities/instances involved when an
VectorLayer is added to a map by calling
QgsMapLayerRegistry.instance().addMapLayer(layer) or alternatively when a
VectorLayer is created/added through iface.addVectorLayer?
Any input/ideas would be very much appreciated.
Kind regards
Carmelo Schumacher
[1] http://giswiki.hsr.ch/QGIS_ArcGIS_REST_API_Connector_Plugin
<http://giswiki.hsr.ch/QGIS_ArcGIS_REST_API_Connector_Plugin>
------------
Carmelo Schumacher
Institut für Software (IFS)
Hochschule für Technik Rapperswil
Oberseestrasse 10, 8640 Rapperswil, CH
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