funciones

Funciones

Algunos ejemplos de funciones Pyhton para usar dentro de expresiones.

Hay que revisar la versión de la API. Seguramente

Primera aproximación al uso de las funciones propias con Python https://geoinnova.org/blog-territorio/funciones-qgis-empezando-con-python/

Using Custom Python Expression Functions https://www.qgistutorials.com/en/docs/custom_python_functions.html

import math
from qgis.core import *
from qgis.gui import *

@qgsfunction(args=0, group='Custom', usesgeometry=True)
def GetUtmZone(value1, feature, parent):
    centroid = feature.geometry()
    longitude = centroid.asPoint().x()
    latitude = centroid.asPoint().y()
    zone_number = math.floor(((longitude + 180) / 6) % 60) + 1

    if latitude >= 0:
        zone_letter = 'N'
    else:
        zone_letter = 'S'

    return '%d%s' % (int(zone_number), zone_letter)

Function editor for QGIS expressions https://nathanw.net/2015/01/19/function-editor-for-qgis-expressions/

User defined expression functions for QGIS https://nathanw.net/2012/11/10/user-defined-expression-functions-for-qgis/

from qgis.utils import qgsfunction
from qgis.core import QGis
 
@qgsfunction(0, "Python")
def vertices(values, feature, parent):
    """
        Returns the number of vertices for a features geometry
    """
    count = None
    geom = feature.geometry()
    if geom is None: return None
    if geom.type() == QGis.Polygon:
        count = 0
        if geom.isMultipart():
          polygons = geom.asMultiPolygon()
        else:
          polygons = [ geom.asPolygon() ]
        for polygon in polygons:
          for ring in polygon:
            count += len(ring)
    return count

How to create custom functios in QGIS using the function editor https://howtoinqgis.wordpress.com/2017/05/20/how-to-create-custom-functions-in-qgis-using-the-function-editor/

@qgsfunction(args='auto', group='Custom')
def factor_area(factor, feature, parent):
    """ This function returns the area of the current geometry multiplied by a user-defined factor. """
    geom_area = feature.geometry().area()
    new_area = factor * geom_area
    return new_area

Best practices for writing Python QGIS Expression Functions http://www.opengis.ch/2017/05/10/best-practices-for-writing-python-qgis-expression-functions/