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I have a large number of small tiles merged into a single VRT. The rasters are only viewed at large scale, so only a few of them are visible at the same time. The map refresh in qgis is slowing down however, as the number of tiles in the vrt increases. Is there any indexing of raster possible in the vrt format itself or perhaps inside pyqgis (manipulating the raster layer that links to my .vrt).

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    Perhaps some of the answers in this post might help: Best way to manage large number of geoTiff rasters. – Joseph Nov 5 '15 at 10:48
  • Seen that. WMS is not an option, its a local desktop application... Also way too much time would be spent retiling additional tiles i think. – U2ros Nov 5 '15 at 10:50
  • Only other thing I could think of would be creating pyramids :) – Joseph Nov 5 '15 at 10:57
  • Also no use, the zoom level at which my raster are used is below the pyramidss, they're not even used. – U2ros Nov 5 '15 at 10:58
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    Your analysis is right and VRT does not support any kind of indexing. There is an open GDAL ticket about this trac.osgeo.org/gdal/ticket/5762. However, there may be a workaround. It should be possible to create a set of smaller .VRT files which contain a reasonable amount of images and then build another vrt from the first generation .VRT files. Sort of a hand written b-tree index. – user30184 Nov 5 '15 at 11:13
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Summarizing the comments so this question can be marked as answered:

VRT does not support any kind of indexing. There is an open GDAL ticket about this http://trac.osgeo.org/gdal/ticket/5762. However, there may be a workaround. It should be possible to create a set of smaller .VRT files which contain a reasonable amount of images and then build another vrt from the first generation .VRT files. Sort of a hand written b-tree index.

ECW might be an alternative, depending on the use case.

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