[GIS] How to control band order generation in GDAL Merge

gdal-mergeqgis

I am trying to merge a total of 8 GeoTiff files (each one representing a single band) into a single TIF file using Gdal Merge in QGIS. The tool works, but does not allow me to select the order that these layers will be compiled in the output file.

This is problematic as the layer names are NOT conserved in the tool, and therefore it is difficult to tell one band from the other after merging (they are just named Band1, Band2).
I have also tried running this in the CMD (since in QGIS you cannot even try to control layer order), but I couldnt get gdal_merge.py to work. The same for running gdal_merge via PyQGIS.

Here is what I mean by not being able to select layer order in the interface:

The problem is the same across QGIS 2.14 and 2.18.

Best Answer

So one solution is in QGIS 3.0, where the exact same tool (GDAL Merge) allows to control the input layers' order by just dragging them above/below each other carefully. Oddly, if you drag a layer 'into' another it deletes it from the Multiple Selection box, so you must put it exactly between the layers you'd like it to appear.

Related Solutions

[GIS] how to rename the band-names of a layer stack

I also needed to know how to rename bands in an open source environment so spent a whole day looking for answers.

There is no way to name bands in QGIS while merging.

But it can be done after the file is created, by editing their .aux.xml file. It works for both .tif and .img files, as far as I've researched.

The solution is to include after each <PAMRasterBand band="1">, <PAMRasterBand band="2">, etc, a subelement <Description>YourBandName</Description>. I haven't tested it for VRT datasets, but the link at the end suggests that it should be the same procedure.

In ArcMap, you will be able to see the new names in the Properties > Symbology window, when setting your colour composite, also in Table of Contents, under your image layer.

In QGIS, I suspect there is a bug, and this will not work. However, you can still label your bands in a more indirect way by also including after the element the subelement:

<Metadata>
   <MDI key="Band">YourBandName</MDI>
</Metadata>

This will show up in the Properties > Metadata tab, for each individual band.

Example image attached, only first band was named for demonstration. Checked on ArcMap on Windows and QGIS in Ubuntu.

Sources: http://lists.osgeo.org/pipermail/gdal-dev/2013-October/037321.html

enter image description here

[GIS] How to batch merge rasters using FOSSGIS tools

Open MSYS (It should have been downloaded along if you used OSGeo4W utility to install qgis)
cd (Change Directory) to your folder with your data.
- cd c:/(path to)/(my data)/ (Hint: pressing tab, autocompletes)
one-line it: gdal_merge.py -o out.tif $(ls *.tif)
- out.tif -> is your output file, name it to whatever you want.
- $(ls *.tif) -> lists all the files ending with tif, and parses it at a parameter to gdal_merge. Change it as needed.

you can explore more options of gdal_merge.py at the relevant page.

Best Answer

Related Solutions

[GIS] how to rename the band-names of a layer stack

[GIS] How to batch merge rasters using FOSSGIS tools

Related Question