What's the correct syntax to use Processing gdalogr:merge from python?

Question

I am using gdalogr:mergein Python console in order to merge to rasters (.tif) But I don't really understand the first parameter, where I have to put two variables.

I get the following error:

Unable to execute algorithm
Wrong parameter value: ras1; ras2

None

import processing   
from processing.core.Processing import Processing
from qgis.core import *
from qgis.gui import *

ras1 =QgsRasterLayer("H:/pyQGIS/DATA_U6/mdt_483.tif","MDT483")
ras2 = QgsRasterLayer("H:/pyQGIS/DATA_U6/mdt_508.tif", "MDT508")

QgsMapLayerRegistry.instance().addMapLayers([ras1])
QgsMapLayerRegistry.instance().addMapLayers([ras2])

merj = processing.runalg("gdalogr:merge",'ras1; ras2', False, False, 4,"H:/pyQGIS/DATA_U6/mdt_mosaico.tif")
print(repr(merj))

Answer 1

The algorithm expects (in the first argument) the input raster paths using a semicolon as separator. Don't add any blank space after the semicolon.

Your script could be just 2 lines long now:

import processing

merj = processing.runalg('gdalogr:merge','H:/pyQGIS/DATA_U6/mdt_483.tif;H:/pyQGIS/DATA_U6/mdt_508.tif', False, False, 4,'H:/pyQGIS/DATA_U6/mdt_mosaico.tif')

It should do the trick. I've tested it with Processing versions 2.10.3 and 2.12.2 on QGIS 2.14.1 (Essen).

Answer 2

Hmm @GermánCarrillo's solution also worked for me. If you want to use ras1 and ras2 as input parameters then you can try the following:

import processing

ras1 = "H:/pyQGIS/DATA_U6/mdt_483.tif"
ras2 = "H:/pyQGIS/DATA_U6/mdt_508.tif"

merj = processing.runalg("gdalogr:merge", ras1 + ";" + ras2, False, False, 4,"H:/pyQGIS/DATA_U6/mdt_mosaico.tif")