Diskussion:Workshop QGIS Python GeoPython 2017: Unterschied zwischen den Versionen

Version vom 9. März 2017, 11:56 Uhr

See also

• https://github.com/simran001/PyQGIS_workshop
• https://etherpad.coredump.ch/p/Python-Workshop

Custom Python Expression Functions for QGIS

Possible examples:

• Function reading from other feature properties
• Function reading from other layers (1:1)
• Functions aka system variables and "Singletons" like layer properties or number sequence (spcial Plugin needed?)
• Function for remote webservice: geocoding (reading from the internet)

Restrictions:

• Relationship other than 1:1
• Reading data from another layer (without own iterator and accessor)

Workflows

• QGIS Basics: Processing data with files, virtual layers, or realtime (= functions)
• How to handle own projects, plugins and functions?
• Use Cases... (see notes)

Notes:

Add attributes from a layer in the project or an external file (csv) to a layer (or the composer?) using insert expression? Create a custom expression python function to do this: http://nathanw.net/2012/11/10/user-defined-expression-functions-for-qgis/

How to import a user defined expression functions on QGIS start up. => Add them to qgis2/python/startup.py

Given polygon layer and a point one, calculate for each polygon feature, the number of points that it covers: https://lists.osgeo.org/pipermail/qgis-user/2016-October/038139.html http://gis.stackexchange.com/questions/212415/referencing-to-features-geometry-in-an-expression/212762#212762

Automatic Field Calculator Plugin: http://plugins.qgis.org/plugins/AutoFields/

Expressions Plus Plugin - Extra functions for the expression engine which didn't make it into QGIS 2.0: https://plugins.qgis.org/plugins/qgsexpressionsplus/

Resource Sharing Plugin (http://plugins.qgis.org/plugins/qgis_resource_sharing/) E.g. https://github.com/mara91/qgis_styles.git