Symbolizing raster layer with Python QGIS

Question

I have a simple Python code that makes some calculations on rasters and give me some output rasters; I have also a style saved to color rasters based on pixel values. Is there an option to load the output (single-band) rasters with the color style I want in stead to have them in black and white?

from qgis.analysis import QgsRasterCalculator, QgsRasterCalculatorEntry
b=[12.158, 13.094, 15.961, 19.553, 24.669, 29.16, 31.805, 31.615, 27.284, 22.286, 17.026, 13.31]
s=['Tmaxjan', 'Tmaxfeb','Tmaxmar','Tmaxapr','Tmaxmay','Tmaxjun','Tmaxjul','Tmaxaug','Tmaxsep','Tmaxoct','Tmaxnov','Tmaxdec']
path = '/Users/macbook/Desktop/TESI/PROGETTO/raster_T_max/'
list=[0,1,2,3,4,5,6,7,8,9,10,11]
for i in list:
 rasterfile = QgsRasterLayer('/Users/macbook/Desktop/TESI/PROGETTO/DEM CAPITANATA.tif')
 entries = []
 ras1 = QgsRasterCalculatorEntry()
 ras1.ref = 'ras@1'
 ras1.raster = rasterfile
 ras1.bandNumber = 1
 entries.append( ras1 )
 new_path = path + s[i]+ '.tif'
 temperature = str(b[i]) + "+" + '(-0.007)' + '* ras@1 '
 Temp = QgsRasterCalculator(temperature, new_path, 'GTiff', rasterfile.extent(), rasterfile.width(), rasterfile.height(), entries )
 Temp.processCalculation()
 iface.addRasterLayer(new_path)

• Kartograaf: You can apply either interpolated, discrete, or exact color ramp depending on your preferences using QgsColorRampShader as shown in this tutorial:opensourceoptions.com/blog/…

Answer 1

If you already have a saved .qml style file which you would like to apply to your loaded raster, you can do it like this. Just change the style_path variable to point to the location of your saved style file:

# ...the previous part of your code
Temp.processCalculation()
# add lines below
rasterlayer = iface.addRasterLayer(new_path)
# change path below to point to your saved style file
style_path = '/Users/macbook/path/to/named_style.qml'
rasterlayer.loadNamedStyle(style_path)
iface.layerTreeView().refreshLayerSymbology(rasterlayer.id())
# (Optional) if you want to expand the layer item in the legend, add the lines below
legenditem = iface.layerTreeView().model().rootGroup().findLayer(rasterlayer)
legenditem.setExpanded(True)

• Rapu93: I tried but anyway, it printed the output rasters in black and white...
• Ben W: @Rapu93, are you sure that you specified the correct path to your .qml file?
• Rapu93: Yes the path is correct

Answer 2

To add a raster layer and then apply a custom style to it:

rasterlayer = iface.addRasterLayer(rasterlayer_path)
rasterlayer.loadNamedStyle(style_path)
iface.layerTreeView().refreshLayerSymbology(rasterlayer.id())
rasterlayer.triggerRepaint()

Where: rasterlayer_path contains the path string of the raster layer and style_path contains the path string of the .qml QGIS Layer Style file.

For more info, see:

• https://docs.qgis.org/3.16/en/docs/pyqgis_developer_cookbook/loadlayer.html#raster-layers
• https://docs.qgis.org/3.16/en/docs/pyqgis_developer_cookbook/raster.html
• https://qgis.org/pyqgis/3.16/core/QgsMapLayer.html#qgis.core.QgsMapLayer.triggerRepaint