[gdal-dev] vrt performance with 1000's of tiles?

[John C. Tull]

On Apr 5, 2010, at 12:33 PM, Matt Klaric wrote:

> 
> On Mon, Apr 5, 2010 at 2:20 PM, William Kyngesburye <woklist at kyngchaos.com> wrote:
> I thinking of creating a vrt for approx 19000 geotiff DEM tiles (SRTM).  Any comments on the performance or practicality of this?  Is there a difference in performance between Geotiff and GRASS as the tile format?
> 
> Mainly it's so I can easily extract regions for projects, so it would be one-shot gdal_translate runs.
> 
> 
> I've done something similar.  
> 
> Check out the SourceProperties tag in http://www.gdal.org/gdal_vrttut.html. If you specify that for each source image, then GDAL doesn't have to open all 19000 images at runtime.  The performance is quite good.  

Looking at the vrt from the file I built with my drg images, I have this:

    <SimpleSource>
      <SourceFilename relativeToVRT="1">./barrett_canyon/o39117a4.tif</SourceFilename>
      <SourceBand>1</SourceBand>
      <SourceProperties RasterXSize="4463" RasterYSize="5710" DataType="Byte" BlockXSize="4463" BlockYSize="1"/>
      <SrcRect xOff="0" yOff="0" xSize="4463" ySize="5710"/>
      <DstRect xOff="92733" yOff="134498" xSize="4473" ySize="5723"/>
    </SimpleSource>

So, presumably, gdalbuildvrt generates this for you. Is there something missing here to achieve what you are talking about, Matt?

Thanks,
John
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