QGIS – Merging Raster Creates BOX with No Data

gdal-mergegeotiff-tiffnodataqgisraster

I have 2 rasters. The first one is a lidar which is clipped by a masked layer. (30.53mb, pixel size=1m,float32)

The other is a local survey GEOTIFF. (75kb, pixel size=1m,float32)

When I merge them, QGIS makes a "box" with no data values. This is the command:

GDAL command:
gdal_merge.bat -a_nodata 0.0 -ot Float32 -of GTiff -o C:/Users/DELL/AppData/Local/Temp/processing_mciOFb/1182dffdfdad4287b941faacdf067b43/OUTPUT.tif –optfile C:/Users/DELL/AppData/Local/Temp/processing_mciOFb/268a4fe4705745a6817ebfd45e67ff3b/mergeInputFiles.txt

What am I missing?

I have done these things for many times and my first time to experience this.

Best Answer

The smaller raster was an output from the Raster Calculator and was not showing the correct extents (showing only positive results). The Raster Calculator produced a box/rectangular raster (including negative results).

This is the reason why there is a box when I merged the two rasters as it included the areas with negative values.

Related Solutions

GDAL – Merging Multiple GeoTIFF’s with gdal_merge Creates Solid Gray GeoTIFF

Gdalbuildvrt it better than gdal_merge.py for most use cases. However, your issue is easy to fix. Gdalinfo shows that source images are paletted, and both are having the same color table

 0: 253,253,253,0
 1: 17,204,142,255
 2: 0,0,0,255
 3: 0,0,0,255
 4: 0,0,0,255
...

From the documentation https://gdal.org/programs/gdal_merge.html:

-pct

Grab a pseudo-color table from the first input image, and use it for the output. Merging pseudo-colored images this way assumes that all input files use the same color table.

So the gdal_merge command to use is

gdal_merge -pct -o result.tif 1.tif 2.tif

How to do the same with gdalbuildvrt:

gdalbuildvrt test.vrt 1.tif 2.tif
gdal_translate test.vrt result.tif

Your original result.tif image is not solid gday. Running gdalinfo result.tif -stats shows that is has values 0 and 1 like the original paletted images have. But because the color table was not copied the image turned into grayscale with totally black and almost black pixels that eye cannot separate.

STATISTICS_MAXIMUM=1
STATISTICS_MEAN=0.012810842015339
STATISTICS_MINIMUM=0
STATISTICS_STDDEV=0.11245765577406
STATISTICS_VALID_PERCENT=100

Best Answer

Related Solutions

GDAL – Merging Multiple GeoTIFF’s with gdal_merge Creates Solid Gray GeoTIFF

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