Diskussion:Workshop QGIS Python GeoPython 2017: Unterschied zwischen den Versionen
Aus Geoinformation HSR
Stefan (Diskussion | Beiträge) K |
Stefan (Diskussion | Beiträge) K (→Using Expression Functions =) |
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| − | === Using Expression Functions | + | === Using Expression Functions === |
Where are Expression Functions used? | 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, Label-Properties, in Field Calculator when creating/updatin fields. |
* Processing => Refactor fields | * Processing => Refactor fields | ||
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# Function for remote webservice: geocoding (reading from the internet). | # Function for remote webservice: geocoding (reading from the internet). | ||
# Function reading from other layers (outlook, rather candidate for a plugin). | # Function reading from other layers (outlook, rather candidate for a plugin). | ||
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=== Writing Expression Functions === | === Writing Expression Functions === | ||
Version vom 9. März 2017, 15:27 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, Label-Properties, in Field Calculator when creating/updatin fields.
- Processing => Refactor fields
How to use:
Possible examples:
- Function doing something "local".
- Function reading from other field(s).
- Functions aka "Singleton" 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 (outlook, rather candidate for a plugin).
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
