gdalwarp for tiling rasters
superbla3000 at GMX.NET
Thu Oct 7 16:39:20 EDT 2004
Jan Hartmann wrote:
> joerg p wrote:
> > hello,
> > I downloaded several overlapping europe etm+ mosaics, reprojected them
> > to geo. Each file is around 1.2 GB. For better performance I know I
> > have to tile them and build overviews.
> > To tile and remove the overlapping, i would like to first combine all
> > images and then to tile them.
> > It's gonna be a really huge file during this process, around 18 GB,
> > does this work?
> > Could someone give me an example of this gdal combine command? I can't
> > find it.
> > How many overview steps should I build, is there a rule of thumb?
> You can use gdalwarp to create tiles from many input files without
> combining these first into one huge file. The thing to remember is that
> gdalwarp can warp *into* an existing output file. In that case, all
> settings of that file (extent, pixel size, projection etc) are
> conserved, and the content of the input file is copied to the
> appropriate locations. Gdalwarp does not need to read complete rasters
> into memory, so you can tile as large a region as you wish.
> So if you use the following gdalwarp parameters
> -te xmin ymin xmax ymax
> -tr xres yres
> you can create as many tiles as you like and fill them with the input
> files. A brute force method would be to warp all input files into all
> output files; a somewhat more clever one would be to check for the
> extent of the input files first and only warp them into the relevant
> output tiles.
> As to the number of overviews: my simple rule of thumb is to resample in
> factors of two: a 10000*10000 raster gets overviews at 5000*5000,
> 2500*2500, 1250*1250 and 625*625. There should be no need to go below
> that. I tile all files in tiles of 2000*2000, although this number is
> perhaps a bit too small. I would appreciate to hear from others how they
> do this.
> Perhaps this functionality of gdalwarp could be explained a bit more in
> detail in the manual page. For now it only says: "Mosaicing into an
> existing output file is supported if the output file already exists".
> This is really a very important and powerful aspect of the program and
> it is very easy to overlook this line. At least that is what I did for a
> considerable length of time.
Thanks a lot for your explanation!
But I thought, since I have lots of overlapping parts, I should first
merge and than tile?
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