Diskussion:Workshop QGIS Python GeoPython 2017: Unterschied zwischen den Versionen
Stefan (Diskussion | Beiträge) K |
Stefan (Diskussion | Beiträge) K |
||
| Zeile 4: | Zeile 4: | ||
''Custom Python Expression Functions for QGIS'' | ''Custom Python Expression Functions for QGIS'' | ||
| + | |||
| + | Background - Where are Expression Functions used? | ||
| + | * Any place | ||
| + | * Processing => Refactor fields | ||
| + | |||
| + | Collected use cases: | ||
| + | * Add new (calculated) field | ||
| + | * Autoincrement / Sequence => QGIS 2.18 default Werte (QGIS 3 geplant) | ||
Possible examples: | Possible examples: | ||
| − | + | # Function reading from other feature properties | |
| − | + | # Functions aka predefined variables (@), "Singletons" like System Env (usage "env('USERNAME')") layer properties or number sequence (spcial Plugin needed?) | |
| − | + | # Function for remote webservice: geocoding (reading from the internet) | |
| − | + | # Function reading from other layers (1:1) | |
| − | |||
| − | |||
| − | |||
| − | |||
| − | |||
| − | |||
| − | |||
| − | |||
Plugins: | Plugins: | ||
Version vom 9. März 2017, 15:05 Uhr
See also
Custom Python Expression Functions for QGIS
Background - Where are Expression Functions used?
- Any place
- Processing => Refactor fields
Collected use cases:
- Add new (calculated) field
- Autoincrement / Sequence => QGIS 2.18 default Werte (QGIS 3 geplant)
Possible examples:
- Function reading from other feature properties
- Functions aka predefined variables (@), "Singletons" like System Env (usage "env('USERNAME')") layer properties or number sequence (spcial Plugin needed?)
- Function for remote webservice: geocoding (reading from the internet)
- Function reading from other layers (1:1)
Plugins:
- ExpressionPlus (for QGIS)
- refFunctions
- spatialJoin
- AutoFields (obsolete)
Writing:
- How to install and share an Expression Function?
- Save and Load in "Function Edtior" (saves to "%USERHOME%.qgis2\python\expressions" (where %USERHOME% under Windows is e.g. "C:\Users\sfkeller\").
- Add Fn. to qgis2/python/startup.py
- Add Fn. to any (own and loaded) QGIS plugin
- Add Fn. to the "Expresion Plus Plugin"
- Debugging:
- use "print"
- use pdb (see QGIS docs and giswiki)
- (use Remote Debug Plugin)
- FAQ
- How to store a value in PyQGIS? Use QSettings (/.qgis) or QGISProject (.qgs)
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
