gdalwarp for tiling rasters

[joerg p]

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.
>
> Jan
>
>

Thanks a lot for your explanation!

But I thought, since I have lots of overlapping parts, I should first
merge and than tile?

Joerg