QGIS python script loop for raster calculator

Question

How can I write a QGIS script for making a loop of raster calculator through a set of rasters? I know I can read multiple raster by applying:

lddLrs = qgis.utils.iface.legendInterface().layers()
for lyr in lddLrs:

And I want to apply an easy operation such as "Raster/Raster*Raster" and repeat it through multiple rasters and get the result with the same name of the input raster with a suffix.

Any Idea?

For using the script to make a new tool within the "processing Toolbox - Scripts - Create New Script" I made the following script but it doesn't work. Any idea to fix it?

##NoDATA Background=name 
##lyr=multiple raster
##OUT=output raster
import qgis
from qgis.analysis import QgsRasterCalculatorEntry, QgsRasterCalculator
# Get layer object
layer = processing.getObject(lyr)
lddLrs = qgis.utils.iface.legendInterface().layers()
for lyr in lddLrs:
 entries = [] 
 ras = QgsRasterCalculatorEntry()
 ras.ref = 'lyr@1'
 ras.raster = lyr
 ras.bandNumber = 1
 entries.append( ras ) 
 calc = QgsRasterCalculator( '("lyr@1" / "lyr@1") * "lyr@1"', +lyr.name() + "_suffix.tif", 'GTiff', lyr.extent(), lyr.width(), lyr.height(), entries )
 calc.processCalculation()

resulting tool

• Joseph: Are you wanting to select individual rasters from the loaded rasters and run the script on those selected? Or do you want the script to apply to all loaded rasters?
• Nico_77: Indeed, the usefulness of making a script by using the Processing Toolbox is the possibility of selecting some or all loaded raster through the tool

Answer 1

You could use something like the following:

import processing
lddLrs = qgis.utils.iface.legendInterface().layers()
path = "path/to/results//"
for lyr in lddLrs:
 processing.runalg("saga:rastercalculator", lyr, None, "(a/a)*a", True, 7, path + lyr.name() + "_suffix.tif")

---

EDIT :

If you want to use the QgsRasterCalculator, you could try using the following (based on this post):

from qgis.analysis import QgsRasterCalculatorEntry, QgsRasterCalculator
lddLrs = qgis.utils.iface.legendInterface().layers()
path = "path/to/results"
for lyr in lddLrs:
 entries = []
 ras = QgsRasterCalculatorEntry()
 ras.ref = 'ras@1'
 ras.raster = lyr
 ras.bandNumber = 1
 entries.append( ras )
 calc = QgsRasterCalculator( '(ras@1 / ras@1) * ras@1', path + lyr.name() + "_suffix.tif", 'GTiff', lyr.extent(), lyr.width(), lyr.height(), entries )
 calc.processCalculation()

---

UPDATE:

You can use the following code in a script which allows you to select individual rasters and run the calculator on them. I've changed the output to a folder so that multiple (or single) rasters can be output to the same directory but you can change this:

##NoDATA Background=name
##Raster=multiple raster
##OUT=folder
import glob, qgis
from PyQt4.QtCore import QFileInfo
from qgis.analysis import QgsRasterCalculatorEntry, QgsRasterCalculator
from qgis.core import QgsMapLayerRegistry, QgsRasterLayer
# Split rasters
layers = Raster.split(';')
output_path = OUT + "/"
suffix = "_suffix.tif"
for ras in layers:
 # Get layer object
 lyr = processing.getObjectFromUri(ras)
 entries = [] 
 ras = QgsRasterCalculatorEntry()
 ras.ref = 'lyr@1'
 ras.raster = lyr
 ras.bandNumber = 1
 entries.append( ras ) 
 calc = QgsRasterCalculator( '(lyr@1 / lyr@1) * lyr@1', output_path + lyr.name() + suffix, 'GTiff', lyr.extent(), lyr.width(), lyr.height(), entries )
 calc.processCalculation()
for results in glob.glob(output_path + "*" + suffix): 
 fileInfo = QFileInfo(results)
 path = fileInfo.filePath()
 baseName = fileInfo.baseName()
 layer = QgsRasterLayer(path, baseName)
 QgsMapLayerRegistry.instance().addMapLayer(layer)

• Nico_77: Actually I need it to get image background as NoDATA instead of Zero
• Nico_77: Is there a way to make it without using SAGA, but with the QGIS Raster Calculator?
• Nico_77: I mean the QgsRasterCalculator function
• Joseph: @Nico_77 - Updated my post =)
• Nico_77: The UPDATE works perfectly. Results are saved and loaded into the workspace.

Answer 2

The solution provided by @Joseph needs some adjustments to work in QGIS 3

from qgis.analysis import QgsRasterCalculatorEntry, QgsRasterCalculator
from qgis.core import QgsProject
lddLrs = [tree_layer.layer() for tree_layer in QgsProject.instance().layerTreeRoot().findLayers()]
path = "path/to/output"
for lyr in lddLrs:
 entries = []
 ras = QgsRasterCalculatorEntry()
 ras.ref = 'ras@1'
 ras.raster = lyr
 ras.bandNumber = 1
 entries.append( ras )
 calc = QgsRasterCalculator( '(ras@1 / ras@1) * ras@1', path + lyr.name() + "_suffix.tif", 'GTiff', lyr.extent(), lyr.width(), lyr.height(), entries )
 calc.processCalculation()