Loading color map from TXT file into raster layer using PyQGIS

Question

I need to configure a pseudocolour symbology of a raster image using a colour map file in txt format using PyQGIS, how can I do it, and what class allows me to access this configuration?

This can be done manually with the buttons located at the bottom of the Layer Properties, in the pseudocolour symbology settings. The buttons highlighted in the image

The text file with the symbology that is generated and can be loaded by QGIS has the following content:

##Archivo de exportación de mapa de colores generado por QGIS INTERPOLATION:INTERPOLATED
0.11247780174017,215,25,28,255,0,1125
0.32547278888523601,253,174,97,255,0,3255
0.53846777603030205,255,255,192,255,0,5385
0.75146276317536798,166,217,106,255,0,7515
0.96445775032043501,26,150,65,255,0,9645

Answer 1

With a useful method QgsRasterRendererUtils.parseColorMapFile you can open your text file and retrieve the shader items for your raster.

import os

from qgis.core import (
    QgsColorRampShader,
    QgsRasterRendererUtils,
    QgsRasterShader,
    QgsSingleBandPseudoColorRenderer
)

os.chdir("/your/folder/with/text/file/")
lyr = iface.activeLayer()  # your raster layer
colormapfile_name = "colormap.txt"

loading, ramp_shader_items, shader_type, errors = QgsRasterRendererUtils.parseColorMapFile(colormapfile_name)

if not loading:
    raise OSError(", ".join(errors))

shader = QgsRasterShader()
ramp_shader = QgsColorRampShader()
ramp_shader.setColorRampType(shader_type)
ramp_shader.setColorRampItemList(ramp_shader_items)
shader.setRasterShaderFunction(ramp_shader)

band = 1
renderer = QgsSingleBandPseudoColorRenderer(
    input=lyr.dataProvider(),
    band=band,
    shader=shader
)
lyr.setRenderer(renderer)
iface.mapCanvas().refreshAllLayers()

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Documentation : QgsRasterRendererUtils