How to make QGIS processing algorithms use default parameter?

Question

My Question is related to: How to make Processing algorithms use default parameter values in QGIS 2.14?

I would like to use gdalogr:translate and only set the values of "INPUT","OUTSIZE","EXPAND" and "OUTPUT".

However, when I run:

processing.runalg('gdalogr:translate', {"INPUT":rlayer,"OUTSIZE":j,"EXPAND":2,"OUTPUT":output})

I get the following error (even tough PROJWIN is not a mandatory parameter):

Error: Missing parameter value for parameter PROJWIN.

I would like to let this parameter as default. When I change the code and include one of the following snippets:

"PROJWIN": ''    OR   "PROJWIN": None

The following error occurs:

Error: Wrong parameter value  for parameter PROJWIN.

Alternatively, I tried setting the paramter PROJWIN to the extent of my current raster layer, without success:

fileInfo = QFileInfo(f)
baseName = fileInfo.baseName()
rlayer = QgsRasterLayer(f, baseName)
e = rlayer.extent()
processing.runalg('gdalogr:translate', {"INPUT":rlayer,"OUTSIZE":j,"EXPAND":2,"PROJWIN":e,"OUTPUT":output})

Does anyone know how this could work?

Answer 1

Not sure if the extent of the layer can be pre-set with a default value when running it from the console. I always define the extent when it is one of the parameters (which I assume is always required):

from PyQt4.QtCore import QFileInfo
import processing

f = iface.activeLayer()
fileName = f.source()
fileInfo = QFileInfo(fileName)
baseName = fileInfo.baseName()
rlayer = QgsRasterLayer(fileName, baseName)

extent = rlayer.extent()
xmin = extent.xMinimum()
xmax = extent.xMaximum()
ymin = extent.yMinimum()
ymax = extent.yMaximum()

output = "C:/Users/You/Desktop/result.tif"
processing.runalg('gdalogr:translate', {"INPUT":rlayer,"OUTSIZE":j,"EXPAND":2,"PROJWIN":"%f,%f,%f,%f"% (xmin, xmax, ymin, ymax),"OUTPUT":output})