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

[John C. Tull]

On Apr 5, 2010, at 1:29 PM, Matt Klaric wrote:

> 
> 
> On Mon, Apr 5, 2010 at 2:52 PM, John C. Tull <jctull at gmail.com> wrote:
> 
> 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?
> 
> 
> That looks very similar to what I have with only one exception.  I'm using an absolute path.  Could it be the case that you created this VRT and have since moved it?  Or the data that it's referring to?  If so, the VRT file may not be able to find the TIFF files that it's pointing to.  
> 
> I'd suggest testing this by using gdal_translate to extract a piece of the VRT where you expect there to exist data.  Run gdal_translate with CPL_DEBUG=ON in your environment so that you can see debug info to understand what files it's trying to open.  You should be able to see it opening one of your TIFF files.....and verbose info if it's failing to.  
> 

It's been a little while since I've revisited this issue. Returning to it, things appear to be working with gdal-1.7.1 for me. The only issue appears to be qgis not rendering it when the view is at a really large scale. This is ok for me because I really only want to see the data at fairly low scales anyway, say 50k and lower.

Thanks for the tips, though, Matt. Relative or full paths both work for me, for the record.

Cheers,
John
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