[gdal-dev] gdalwarp to VRT. How to set "-multi" option? How to get best performances when chaining gdal operations?

[Even Rouault]

Daniele,

It is not possible to use -multi with warped VRT. The VRTWarpedDataset uses a 
lower-level API than the gdalwarp utility. The gdalwarp utility processing the 
whole dataset (or a subwindow known in advance), it can optimize things by 
fetching the input data from the next chunk while the current one is heating 
your CPU... On the contrary the VRTWarpedDataset warps the blocks only when 
there are requested, so there's no trivial possibility to optimize this.

Best regards,

Even

Le jeudi 13 janvier 2011 11:07:24, Daniele Romagnoli a écrit :
> Hi list,
> I have a thousand of file with SRS A which I will to mosaic, reproject to
> SRS B and then retile (I will use GDAL 1.7.2).
> 
> What I will do is:
> 1- setting up a VRT using gdalbuildvrt on top of the original TIF files.
> 2- reprojecting it to an intermediary VRT using gdalwarp (to SRS B).
> 3- retiling the reprojected VRT as 32768x32768 (or something smallers)
> geotiffs with gdal_retile by also adding JPEG compression, inner 512x512
> tiling and bicubic interpolation on intermediate levels
> 
> How can I get best performances with this operations chaining?
> 
> >From [1], I see I can play with "--config GDAL_CACHEMAX xxxx -wm xxxx"
> >when
> 
> invoking gdalwarp. (I will set GDAL_CACHEMAX as an environment var)
> I see that the wm parameter as well as inner tiling are set on the
> reprojected.vrt as GDALWarpOptions.
> Is there a way to set the "-multi" parameter in the reprojected vrt too to
> make use of this feature to separate thread for I/O and thread for
> computation?
> 
> Regards,
> Daniele
> 
> [1]: http://trac.osgeo.org/gdal/wiki/UserDocs/GdalWarp