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I am hoping to find a relatively straightforward way to create a virtual raster for a large set of rasters (c. 15,000 TIF files from the TQ 100K Square of OS 1-10K).

I cannot do this in QGIS. I get the following error: "The process failed to start. Either the invoked program is missing, or you may have insufficient permissions to invoke the program". Presumably this is because there are too many files: it works fine for other squares with fewer files.

I have attempted copying and pasting the script that QGIS generates into OSGeo4W Shell, and running it there without success. I have run this at the root of the drive (H:>), the destination folder for the virtual raster, and the folder containing the source tifs. Clearly I am doing something wrong, but I do not have the expertise to know what, or how to remedy it.

The script I get is: gdalbuildvrt "//..../My Documents/GIS/Datasets/Ordnance Survey/1-10,000/2018/Virtual Rasters/1-10K_TQ.vrt" "...list of files..."

Is it possible to do this through OSGeo4W Shell, or do I just need to break it down into smaller chunks and run it through QGIS?

I have tried numerous pieces of advice on here and elsewhere, e.g. https://astuntech.atlassian.net/wiki/spaces/ISHAREHELP/pages/14844053/Mosaic+thousands+of+raster+images, but they are either not specific enough to my situation, or require a level of understanding of script which I do not have.

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    that wiki page assumes you are on a unix box – Ian Turton♦ Mar 2 '18 at 17:09
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You need to generate a file containing a list of the tiffs one per line:

dir /b /s H:\My Documents\GIS\Datasets\Ordnance Survey\1-10,000\2018\TQ\*.tif > files.txt

Here you are using the standard windows dir command to list all the .tif files into a file called files.txt. (/b removes the header/footer, and /s makes it recursive). This allows you to avoid the command line length limit by passing that file to gdalbuildvrt using the -input_files_list option: 

gdalbuildvrt -input_file_list files.txt 1-10K_TQ.vrt

Since you used a full path in the file names list you can use it anywhere and just create the vrt where you need it.

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  • Sorry Ian, you're going to have to unpack that for me a bit more please: the tiffs are contained in the folder: H:\My Documents\GIS\Datasets\Ordnance Survey\1-10,000\2018\TQ - I've tried inserting that into the 1st piece of script you have written there, with no joy, but then I am probably doing this wrong. Please could you clarify what I should be entering here? – JimS-W Mar 2 '18 at 17:21
  • Still not working I'm afraid: keeps saying "The system cannot find the path specified". Should I literally be pasting: dir /b /s H:\My Documents\GIS\Datasets\Ordnance Survey\1-10,000\2018\TQ*.tif > files.txt into H:\> ? – JimS-W Mar 2 '18 at 17:42
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    alternatively test it out in smaller steps: dir My Documents then dir My Documents\GIS etc to see where the path is wrong – Ian Turton♦ Mar 2 '18 at 17:43
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    If it's still complaining about not finding the path, maybe try "H:\Users\yourusernamehere\Documents". The spaces in the pathname could be another culprit, you could try double-quoting the whole pathname part too like: "H:\My Documents\GIS\Datasets\Ordnance Survey\1-10,000\2018\TQ*.tif" – cm1 Mar 2 '18 at 19:32
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    can you get dir to list the files at all? – Ian Turton♦ Mar 5 '18 at 13:16

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