Diskussion:Workshop QGIS Python GeoPython 2017
See also
Custom Python Expression Functions for QGIS
Possible examples:
- Function reading from other feature properties
- Function reading from other layers (1:1)
- Functions aka "Singletons", like layer properties or sequence
- 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 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
