Seeking algorithm in QGIS Process Modeller to create vector grid?

Question

I am using Process Modeller to automate merging several vector layers and then creating a grid to cover the extent of the merged layer. There are functions which already exist which are not listed in the modeller such as :

Vector -> Research Tools -> Vector Grid

MMQGIS -> Create -> Create Grid Layer

The QGIS geoalgorithm Create grid in the modeller is not useful to me as I have to manually determine the position and set the CRS etc beforehand.

Is there any other plugin or function which allows me to accomplish this?

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I am now trying to get the Processing plugin (formerly Sextante) to recognise the Vector Grid script. The file is named "doVectorGrid" which I renamed to simply "VectorGrid". I followed this advice: http://planet.qgis.org/planet/tag/sextante/ where it mentions at the bottom how to add your own modified algorithm.

I have added the new terms into the QGISAlgorithmProvider.py (the equilavent to FToolsAlgorithmProvider.py) but I get the following error: ImportError: cannot import name VectorGrid

I'm guessing I have to change the code of the Vector Grid script but I am new to Python. I have copied the ui_frmVectorGrid.py file into the same directory.

Answer 1

There's been somewhat of a development in QGIS since I asked this question back in 04/2014 so will post an answer to close off this question.

The following code does what I had wanted (practically similar to the "Hex grid from layer bounds" script but this wasn't available at the time):

##Create Grid=name
##layer=vector
##cellsize=number 1000
##grid=output vector

input = processing.getObject(layer)

extent = input.extent()
xmin = input.extent().xMinimum() - cellsize / 2
xmax = input.extent().xMaximum() + cellsize / 2
ymin = input.extent().yMinimum() - cellsize / 2
ymax = input.extent().yMaximum() + cellsize / 2
crs = input.crs().authid()

processing.runalg('qgis:creategrid', 1, "%f, %f, %f, %f "% (xmin, xmax, ymin, ymax), cellsize, cellsize, crs, grid)