PyQGIS: Create raster layer from QgsRasterFileWriter

Question

I would like to create a singleBand raster (grayScale) using the method qgis.core.QgsRasterFileWriter.writeRaster

According to the documentation:

writeRaster(self, 
    pipe: QgsRasterPipe, 
    nCols: int,
    nRows: int,  
    outputExtent: QgsRectangle, 
    crs: QgsCoordinateReferenceSystem, 
    feedback: QgsRasterBlockFeedback = None
) → QgsRasterFileWriter.WriterError

You may be agree that this documentation is very unclear on how to use it... I success to create vectorLayer from QgsVectorFileWriter.writeAsVectorFormat.

But there is too few examples on internet using QgsRasterFileWriter...

Here is the example script I have for the moment:

import os
import numpy
from qgis.core import (
    QgsMapLayer,
    QgsRasterFileWriter,
    QgsCoordinateReferenceSystem,
    QgsRectangle,
    Qgis,
)


def write_to_geotiff(data: list, filename: str, epsg: str, layer: str=None) -> None:
    
    x_data = data[0]
    y_data = data[1]
    z_data = data[2]
    
    nx, ny = len(x_data), len(y_data)

   ##########
   # CODE HERE
   ##########

I saw this solution to create a raster but I don t want to use GDAL because off env issues related to GDAL...

Answer 1

I get it using the method QgsRasterFileWriter.createOneBandRaster creating a provider. You can get the bloc of the provider of type QgsRasterBlock and use the method setValue to associate values.

    writer = QgsRasterFileWriter(filename)
    provider = QgsRasterFileWriter.createOneBandRaster(
        writer,
        dataType=Qgis.Float32,
        width=nx,
        height=ny,
        extent=QgsRectangle(
            min(x_data),
            min(y_data),
            max(x_data),
            max(y_data)
        ),
        crs = QgsCoordinateReferenceSystem(f"epsg:{epsg}"),
    )
    provider.setNoDataValue(1, -1)
    provider.setEditable(True)
    
    block = provider.block(
        bandNo=1,
        boundingBox=provider.extent(),
        width=provider.xSize(),
        height=provider.ySize()
    )
    
    for ix in range(nx):
        for iy in range(ny):
            value = z_data[ix][iy]
            if value == numpy.nan:
                continue
            block.setValue(iy, ix, value)
    
    provider.writeBlock(
        block=block, 
        band=1,
        xOffset=0,
        yOffset=0
    )
    provider.setEditable(False)
    

This will create a tiffile: