Import GRASS and SAGA modules to python script

Question

I'm new at this. I am "building" a python plugin for qgis and I want to import modules from GRASS and SAGA but I don't understand how to do it. The plugin I want to import is Kriging interpolation from SAGA or v.surf.idw from GRASS or interpolation plugin from Raster qgis. I want an interpolation method to convert points in grid.

Can you help me?

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I have another doubt.

I run these lines in my code:

vectorlayer_vector =  ftools_utils.getVectorLayerByName(inputLayer)
Elevation = self.lineAttrib.currentText()
cellSize = int(self.linePix.value())
outPath = self.inputLayerCombo3.text()
output = ftools_utils.getRasterLayerByName(outPath) 

Processing.runAlgorithm("saga:shapestogrid", vectorlayer_vector, Elevation, 0, 0, 4, None, cellSize, output)

When I run, I get an tiff image but with nothing. The .aux file is not created and when I try to open the tiff image that I created appears this message:

c:...teste3.tif is not a supported raster data source

So, I guess that the output is wrong. What I have to do to get a correct output? What I missing?

Answer 1

The Processing framework in QGIS can call these function directly from Python.

From the QGIS Python console:

>>>import processing
>>>outputs_0=Processing.runalg("saga:ordinarykriging", vectorlayer_pointtable, z, True, 0, 0, True, 100, True, 0.0, 10.0, 100.0, 1.0, 0.1, 1, 0.5, 1000.0, 4, 20, 1.0, True, None, None, None)
>>>outputs_1=Processing.runalg("grass:r.surf.idw", outputs_0['GRID'], 12, True, None, 0.0, None)

If you build it as a model in the Processing Framework, you can save that model as a Python script. It gives you a kind of GUI builder for the processing runalg function.