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`processing]improved doc of example algorithm
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volaya committed Sep 14, 2013
1 parent 99857bc commit 73dc9c479d93f69823b9f87e1d8f10a63f955ec0
Showing with 24 additions and 7 deletions.
  1. +24 −7 python/plugins/processing/algs/
@@ -36,9 +36,9 @@ class SaveSelectedFeatures(GeoAlgorithm):
'''This is an example algorithm that takes a vector layer and creates
a new one just with just those features of the input layer that are
It is meant to be used as an example of how to create your own SEXTANTE
It is meant to be used as an example of how to create your own Processing
algorithms and explain methods and variables used to do it.
An algorithm like this will be available in all SEXTANTE elements, and
An algorithm like this will be available in all Processing elements, and
there is not need for additional work.
All geoprocessingalgorithms should extend the GeoAlgorithm class'''
@@ -51,7 +51,11 @@ class SaveSelectedFeatures(GeoAlgorithm):

def defineCharacteristics(self):
'''Here we define the inputs and output of the algorithm, along
with some other properties'''
with some other properties.
This will give the algorithm its semantics, and allow to use it in the modeler.
As a rule of thumb, do not produce anything not declared here.
It will work fine in the toolbox, but it will not work in the modeler.
If that's what you intend, then set self.showInModeler = False'''

#the name that the user will see in the toolbox = "Save selected features"
@@ -70,8 +74,13 @@ def processAlgorithm(self, progress):
'''Here is where the processing itself takes place'''

#the first thing to do is retrieve the values of the parameters
#entered by the user
#entered by the user.
#The getParameterValue will return the value with its corresponding type,
#strings in the case of inputs and outputs
inputFilename = self.getParameterValue(self.INPUT_LAYER)

#The output. It will get the value of the destinatation file entered by the user.
#If the user select "Save to temporary file", when we arrive here it will already have an asigned value, which will be
output = self.getOutputFromName(self.OUTPUT_LAYER)

#input layers values are always a string with its location.
@@ -83,16 +92,24 @@ def processAlgorithm(self, progress):

#First we create the output layer.
#To do so, we call the getVectorWriter method in the Output object.
#That will give as a ProcessingVectorWriter, that we can later use to add features.
#That will give us a VectorWriter, that we can later use to add features.
provider = vectorLayer.dataProvider()
writer = output.getVectorWriter( provider.fields(), provider.geometryType(), )
writer = output.getVectorWriter( provider.fields(),
#this is the layer crs. By default all resulting layers are
#assumed to be in the same crs are the inputs, and will be loaded
#with this assumptions when executed from the toolbox.
#The variable has to be canged in case this is not true,
#or in case there are no input layer from which the output crs can be infered )

#Now we take the selected features and add them to the output layer
features = vector.features(vectorLayer)
total = len(features)
i = 0
for feat in features:
for i, feat in enumerate(features):
#we use the progress object to communicate with the user
progress.setPercentage(100 * i / float(total))
i += 1
del writer

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