SzieberthAdam

CREATE OR REPLACE FUNCTION st_extend (
    geom geometry,
    head_rate double precision,
    head_constant double precision,
    tail_rate double precision,
    tail_constant double precision)
  RETURNS geometry AS
$BODY$
-- Extends a linestring.
-- First segment get extended by length * head_rate + head_constant.

SzieberthAdam

def activate_visibility_preset(preset_name, *, project=None, coll=None):
  """Activates a visibility preset by its name.
  Return a boolean indicating success."""
  # https://github.com/qgis/QGIS/blob/f044c95fd8927d86967ce8af3930bdc7523095fa/src/app/qgsmapthemes.cpp#L138
  if project is None:
    project = qgis.core.QgsProject.instance()
  if coll is None:
    coll = project.mapThemeCollection()
  if not coll.hasMapTheme(preset_name):
    return False

SzieberthAdam

# It is assumed that the layer has both "labelX" and a "labelY" attributes set as real number fields.

# Labels / Placement / Data Defined / Coordinate / X:
CASE WHEN  "labelX"  IS NULL THEN toreal(regexp_substr(geom_to_wkt(centroid($geometry)), '(-?\\d+\\.?\\d*) -?\\d+\\.?\\d*')) ELSE "labelX" END

# Labels / Placement / Data Defined / Coordinate / Y:
CASE WHEN  "labelY"  IS NULL THEN toreal(regexp_substr(geom_to_wkt(centroid($geometry)), '-?\\d+\\.?\\d* (-?\\d+\\.?\\d*)')) ELSE "labelY" END

# Labels / Placement / Data Defined / Alignment / horizontal:
'Center'

SzieberthAdam

# project
project_crs = qgis.utils.iface.mapCanvas().mapRenderer().destinationCrs()
qgis.utils.iface.mapCanvas().mapRenderer().setDestinationCrs(new_project_crs)

SzieberthAdam

A gyógyszer tanított meg arra, hogy beteg legyek.
Az idő lejár; a cserebogár marad sárga cserebogár.

SzieberthAdam

# QgsFields() of QgsVectorLayer()
# fields = layer.fields()  # from QGIS 1.12+
fields = layer.pendingFields()  # and below...

# list QgsField() from QgsFields()
fieldlist = fields.toList()

# list of layer fieldnames
[f.name() for f in fieldlist]