[gdal-dev] Problem using gdalbuildvrt with a large number of source datasets

[Homme Zwaagstra]

Hello Jukka,

On 03/12/14 10:13, Jukka Rahkonen wrote:
> Homme Zwaagstra <hrz  <at> geodata.soton.ac.uk> writes:
 >
 >>
 >> Hello,
 >>
 >> I've come up against a problem with `gdalbuildvrt` taking a long 
time to
 >> create
 >> a VRT when it is passed a large number of source datasets. I am trying
 >> to create
 >> a VRT file for a zoom level in a TMS structure containing JPEG 
tiles.  The
 >> command I'm using is:
 >>
 >> gdalbuildvrt output.vrt `find ./tiles/18 -iname *.jpg -printf "%p "`
 >>
 >> where the number of tiles is:
 >>
 >> $ find ./tiles/18 -iname *.jpg | wc -l
 >> 767104
 >
 > I would say that you are doing all wrong thing. First, the jpeg tiles in
 > tile service directory structure are not referenced with world files 
(.jgw)
 > or anything and your .vrt file would be useless.

Sorry, I should have said: each of the JPEG tiles has an accompanying
`*.aux.xml` file.  The files were created under the hood by GDAL using
<https://github.com/geo-data/cesium-terrain-builder#ctb-tile>.

> The right thing to do is to  study the file naming schema that the cache is
 > using. When the schema is known the right tile can be found directly 
because
 > the logic knows how the tile directory structure is like and which 
names are
 > used for the tiles. If it is an OSGeo TMS schema it is described here
 > 
http://wiki.osgeo.org/wiki/Tile_Map_Service_Specification#TileMapService_Resource

The on-disk tiling scheme conforms to
<http://wiki.osgeo.org/wiki/Tile_Map_Service_Specification#global-mercator> 
with
the tile directory structure matching `{zoom}/{x}/{y}.jpg`.

Best regards,

Homme

>
 > If it is using the Google/Bing tile naming schema then you can find 
examples
 > here http://www.gdal.org/frmt_wms.html. But if it is a GeoWebCache tile
 > cache you may be out of luck because I haven't seen so far any 
configuration
 > file that would make GWC tilecache usable for GDAL.
 >
 > -Jukka Rahkonen-
 >
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 > gdal-dev at lists.osgeo.org
 > http://lists.osgeo.org/mailman/listinfo/gdal-dev


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