Diskussion:Workshop QGIS Python GeoPython 2017: Unterschied zwischen den Versionen
Aus Geoinformation HSR
Stefan (Diskussion | Beiträge) K |
Stefan (Diskussion | Beiträge) K |
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''Custom Python Expression Functions for QGIS'' | ''Custom Python Expression Functions for QGIS'' | ||
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| + | === Using Expression Functions ==== | ||
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| + | Where are Expression Functions used? | ||
* Any place where expressions are allowed, e.g. in Attribute Table as Select-Filter, in Field Calculator when creating/updatin fields. | * Any place where expressions are allowed, e.g. in Attribute Table as Select-Filter, in Field Calculator when creating/updatin fields. | ||
* Processing => Refactor fields | * Processing => Refactor fields | ||
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# Function reading from other layers (1:1) | # Function reading from other layers (1:1) | ||
| − | === Writing === | + | |
| + | === Writing Expression Functions === | ||
How to install and share an Expression Function? | How to install and share an Expression Function? | ||
Version vom 9. März 2017, 15:18 Uhr
See also
Custom Python Expression Functions for QGIS
Using Expression Functions =
Where are Expression Functions used?
- Any place where expressions are allowed, e.g. in Attribute Table as Select-Filter, in Field Calculator when creating/updatin fields.
- Processing => Refactor fields
- See http://docs.qgis.org/testing/en/docs/user_manual/working_with_vector/expression.html?highlight=expression
Possible examples:
- Function reading from other feature properties
- Functions aka predefined variables ("@layer_name"), "Singletons" like system environment variables (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)
Writing Expression Functions
How to install and share an Expression Function?
- Save and (Re-)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 the "Expresion Plus Plugin"
- Add Fn. to any (own and loaded) QGIS plugin
Debugging:
- use "print"
- use pdb (see QGIS docs and giswiki)
- (use Remote Debug Plugin)
Notes
Collected (special) use cases:
- Autoincrement / Sequence => QGIS 2.18 default Werte (QGIS 3 geplant)
- 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
- 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/
Plugins:
- ExpressionPlus (for QGIS) Extra functions for the expression engine which didn't make it into QGIS 2.0: https://plugins.qgis.org/plugins/qgsexpressionsplus/
- refFunctions
- spatialJoin
- AutoFields (obsolete) - Automatic Field Calculator Plugin: http://plugins.qgis.org/plugins/AutoFields/
Open:
- How to store a value in PyQGIS? Use QSettings (/.qgis) or QGISProject (.qgs)
- Resource Sharing Plugin (http://plugins.qgis.org/plugins/qgis_resource_sharing/). e.g. https://github.com/mara91/qgis_styles.git
