[Gdal-dev] create 256x256 tiles for google maps

[Jan Hartmann]

Markus Neteler wrote:
> On Thu, Apr 05, 2007 at 09:43:57PM +0200, Mateusz Loskot wrote:
>> Paul Van Deusen napisa?(a):
>>> I am using imagemagick to crop a geotiff file into 256x256 gif files to
>>> serve as tiles for google maps.
>>> However, it starts to choke once the tiff file gets larger than  1/2
>>> GB.   Can gdal_translate take
>>> a tif file and split it into individual tile files of a specific size?
>> Paul,
>>
>> AFAIK, GDAL won't help here out of the box.
>> Users usually take gdal_translate.cpp program and customize it to do this
>> job.
>> Here you can find such utility called gdalsplit and posted to the list a
>> longer while ago:
>>
>> http://lists.maptools.org/pipermail/gdal-dev/2004-September/004135.html
>>
>> May be it will work for you.
> 
> If anyone happens to haave an updated version of "gdalsplit"
> I would be interested.
> Maybe some mechanism to manage user contributions would be
> good (like the GRASS Addons repository).
> 
> Markus
> 
> ------------------
> ITC -> dall'1 marzo 2007 Fondazione Bruno Kessler
> ITC -> since 1 March 2007 Fondazione Bruno Kessler
> ------------------
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> 

Perhaps I am overlooking something, or didn't understand the question 
right, but I regularly create tiles from a large tif-file with the 
-srcwin <xoff yoff xsize ysize> parameter of gdal_translate. A simple 
bash-script to tile in.tif (30000*30000 pixels) into 256*256 tiles would be:

width=30000
height=30000
y=0
while [ $y -lt $height ]
do
   x=0
   while [ $x -lt $width ]
   do
      outtif=t_${y}_$x.tif
      gdal_translate -srcwin $x $y 256 256 in.tif $outtif
      let x=$x+256
   done
   let y=$y+256
done

This would result in about 14000 files. This is so simple that it can 
even be done with a primitive DOS batch file.

Most of the time I work with projected coordinates (-projwin instead of 
-srcwin) but the idea is the same. Note by the way that -projwin uses 
the *upper* left corner as reference.

Jan

Dr. J. Hartmann
Department of Geography
University of Amsterdam