Alessandro et al.,
I'm also interested in using python and QGIS for simple scripts
espacially for batch processing, and some examples could be very useful!
Attached is a python script for performing some basic geoprocessing
functions on vector layers. The header of the file contains usage
examples to help get you started... it's probably not the cleanest
python code, nor the most pythonistic... but you get the idea ;-)
Hope this helps to get you started...
The other good resource for python scripting is:
http://wiki.qgis.org/qgiswiki/PythonBindings
Cheers,
Carson
Thanks
Ale
georgew ha scritto:
ThanKs Alex, the problem is I have not been able to find any example
that is free standing, all seem to be plugins or use QT to generate a
UI. Can you point me to a working example, however simple (e.g. read
shapefile, project,write shapefile) that can set me off on the right
path?
Many thanks
G.
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--
Carson J. Q. Farmer
ISSP Doctoral Fellow
National Centre for Geocomputation (NCG),
National University of Ireland, Maynooth,
Email: carson.far...@gmail.com
Web: http://www.carsonfarmer.com/
http://www.ftools.ca/
from PyQt4.QtCore import *
from qgis.core import *
class GeoprocessingEngine( ):
'''
USAGE:
GeoprocessingEngine( func, layerA, layerB, outPath, encoding, param, merge )
func : geoprocessing function
1: Buffer
2: Convex Hull
3: Difference
4: Dissolve
5: Intersection
6: Union
7: Symetrical Difference
8: Clip
layerA : QgsVectorLayer
layerB : QgsVectorLayer
outPath : string - /home/cfarmer/Desktop/test.shp
encoding : default is 'System'
param : a parameter, may be used for buffer, and dissolve
merge : should the results be merged (buffer)
EXAMPLE:
# import engine
from Geoprocessing import GeoprocessingEngine
layerA = QgsVectorLayer(/path/to/layer.shp, layerA, ogr)
layerB = QgsVectorLayer(/path/to/layer.shp, layerB, ogr)
# create geo engine
geo = GeoprocessingEngine( 5, layerA, layerB, '/home/cfarmer/Desktop/test.shp')
# compute geoprocessing event, and output result
outlayer = geo.compute() # compute() returns the output layer as a QgsVectorLayer
This alows us to link multiple runs together:
geo1 = GeoprocessingEngine( 5, layerA, layerB, '/home/cfarmer/Desktop/test1.shp')
outlayer = geo1.compute()
geo2 = GeoprocessingEngine( 3, layerA, outlayer, '/home/cfarmer/Desktop/test2.shp')
outlayer = geo2.compute()
...
...
temp files are created for better usage of memory when using large layers
'''
def __init__( self, function, layerA, layerB, outputName, encoding = 'System', param = 0, merge = False ):
self.myFunction = function
self.success = False
self.layerA = layerA
self.layerB = layerB
self.param = param
self.merge = merge
self.outputName = outputName
self.encoding = encoding
def compute( self ):
check = QFile( self.outputName )
if check.exists():
if not QgsVectorFileWriter.deleteShapeFile( self.outputName ):
return None
self.geoprocessing( self.myFunction, self.layerA, self.layerB, self.param, self.merge, self.outputName, self.encoding )
return QgsVectorLayer( self.outputName, temp, ogr )
def geoprocessing( self, function, myLayerA, myLayerB, myParam, myMerge, myName, myEncoding ):
self.myFunction = function
self.myLayerA = myLayerA
self.myLayerB = myLayerB
self.myParam = myParam
self.myMerge = myMerge
self.myName = myName
self.myEncoding = myEncoding
self.vlayerA = self.myLayerA
if self.myFunction == 1 or self.myFunction == 2 or self.myFunction == 4:
( self.myParam, useField ) = self.checkParameter( self.vlayerA, self.myParam )
if not self.myParam is None:
if self.myFunction == 1:
geos, feature, match = self.buffering( useField )
elif self.myFunction == 2:
geos, feature, match = self.convex_hull( useField )
elif self.myFunction == 4:
geos, feature, match = self.dissolve( useField )
else:
self.vlayerB = self.myLayerB
if self.myFunction == 3:
geos, feature, match = self.difference()
elif self.myFunction == 5:
geos, feature, match = self.intersect()
elif self.myFunction == 6:
geos, feature, match = self.union()
elif self.myFunction == 7:
geos, feature, match = self.symetrical_difference()
elif self.myFunction == 8:
geos, feature, match = self.clip()
def buffering( self, useField ):
GEOS_EXCEPT = True
FEATURE_EXCEPT = True
vproviderA = self.vlayerA.dataProvider()
