[GIS] Merge two rasters with no data value

gdalgrassnodataqgisraster

I have two rasters: Raster A and B. Raster A has has only values of 0. The white area in Raster B are No Data values. I want to merge them to one raster (Raster C). So basically I want all pixels in Raster B with a No Data value to have a value of 0.

I tried to do this with the raster calculator in QGIS by adding Raster A to Raster B, but it only returns again Raster B.

I am looking for solutions with QGIS, GDAL, or Grass GIS.

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Best Answer

One solution may be this batch script:

set nodatavalue=-99999
gdalwarp -srcnodata None rasterB_with_NoData.tif rasterB_without_NoData.tif
python gdal_calc.py -A rasterB_without_NoData.tif --outfile=rasterB_updated_with_NoData.tif --calc="(A<>%nodatavalue%)*A"
gdalwarp -srcnodata None rasterB_updated_with_NoData.tif rasterB_updated_without_NoData.tif

The trick is -srcnodata None offered by gdalwarp, which is very useful in order to ignore intrinsic nodata settings on the source dataset (from the doc). In detail, we need to apply it two times: firstly because we need to substitute the NoData value with 0 and so we have to include it in the calculation, secondly because gdal_calc.py introduces NoData value again.

Related Solutions

[GIS] Calculating difference two rasters through gdal

I know this is a bit late but might help someone who stumbles upon this question:

https://www.gdal.org/gdalcompare.html

Alternatively, you could use gdal_calc.py with both rasters A and B, and --calc="A-B", then simply check if the min/max values are both 0. If they're not, you can use the result to find out where they differ.

[GIS] pyQGIS Merge raster layers

You don't need processing to execute gdal_tools you can use subprocess module to execute your command. Even Processing use the subprocess so why don't you ? here a function to use it :

import sys
from subprocess import Popen, PIPE, STDOUT
# Create a class herit from Exception class
class ProcessException(Exception):
    pass
# function to run the command
def execute(command):

    process = Popen(command.split(" "), shell=True, stdout=PIPE, stderr=STDOUT, stdin=PIPE)
    # Poll process for new output until finished
    while True:
        nextline = process.stdout.readline()
        if nextline == '' and process.poll() is not None:
            break
        # You can add here some progress infos

    output = process.communicate()[0]
    exitCode = process.returncode

    if (exitCode == 0):
        return output
    else:
        raise ProcessException(command, exitCode, output)

To use it :

try:
    execute(u"gdal_merge.py -n 0 -a_nodata 0 -of GTiff -o /path/of/your/output/mozaik.tif /path/of/your/input/terrain_corrected01.tif /path/of/your/input/terrain_corrected02.tif")
except ProcessException as p:
    print(u"something goes wrong : {}".format(p))

--EDIT-- Where is those command

Gdal comes with QGIS as you install QGIS. In Windows they are in the :

C:\path\of\OSGEO4W\bin\

In linux it's in the :

/usr/bin/
# for the manual
/usr/share/man/manl/gdal_merge.l.gz

In my opinion if you don't need the QGIS API it will be faster and easy to use it in a bash script. But it depends on your need.

Best Answer

Related Solutions

[GIS] Calculating difference two rasters through gdal

[GIS] pyQGIS Merge raster layers

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