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This is similar to a question asked by someone else, re OS tiles, however, there is a difference! I am a bit of a amateur in GIS and python, but if I take it slow I can usually just about work it out!

This one though: I have a large amount(over 10k) of geo-refd png files which I have mosaicked in Arc, but also want to be able to access them in other programs such as QGIS over the web and within a private network using Geoserver - so I have tried creating VRT's with them, and sometimes it works, but sometimes it doesn't: it seems that on selecting over 200-odd png's, the vrt stops being created: is there a limit on the amount of rasters for a VRT, or can some-one give me some help please!! This is so frustrating ;o) The error message is: "The process failed to start. Either the invoked program is missing, or you may have insufficient permissions to invoke the program."

and the code is:

    gdalbuildvrt -allow_projection_difference 
    "F:/Historic Buildings/GIS/Data/Mapping/Landranger/Raster/15k/Data/SX/SX.vrt" 
    "F:/Historic Buildings/GIS/Data/Mapping/Landranger/Raster/15k/Data/SX/1.png" 
    "F:/Historic Buildings/GIS/Data/Mapping/Landranger/Raster/15k/Data/SX/2.png" 
    "F:/Historic Buildings/GIS/Data/Mapping/Landranger/Raster/15k/Data/SX/3.png" 
    "F:/Historic Buildings/GIS/Data/Mapping/Landranger/Raster/15k/Data/SX/4.png" 
    "F:/Historic Buildings/GIS/Data/Mapping/Landranger/Raster/15k/Data/SX/5.png" 
    "F:/Historic Buildings/GIS/Data/Mapping/Landranger/Raster/15k/Data/SX/6.png" 
    "F:/Historic Buildings/GIS/Data/Mapping/Landranger/Raster/15k/Data/SX/7.png"

with an additional +200 similarly addressed png's

I am using QGIS 1.8.0 Lisboa, on W7 64bit

Any help would be gratefully received

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Have you tried it sucessfully with a handfull of files?

For me, it worked with 300 files. At first, I had to build individual vrts for each image to expand the colour information to rgba:

for %%N in (D:\Karten\gdal\gdal2tiles\NL25\*.tif) DO gdal_translate -of vrt -expand rgba %%N D:\Karten\gdal\gdal2tiles\NL25\%%~nN.vrt

Second run, I merged all those vrts to a single one:

gdalbuildvrt -allow_projection_difference index25.vrt NL25\*.vrt

Maybe the command line arguments are limited in character size, which I got around by using the wildcards.

share|improve this answer
Hey AndreThanks for this - yes, I create the vrt with upto about 200 or so files, but after that it seems to refuse. I will ahve a play around with the code, and see if I can save some time and expand the colour on a group, and then merge - I was having a problem merging them, as they were all resulting in blackness, so thanks also for the help/tip re merging and creating rgba's beforehand! – Simonrp Mar 9 '13 at 11:45
I will report back when I have a play around - it wont be for a couple of days though as have a busy weekend ahead! – Simonrp Mar 9 '13 at 11:46

Andre Joost had the correct answer in his last statement.

Its a character limit. If you use the wildcard it runs fine. I just tried on 28000 tiffs and it ran no problem.

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