[FWTools] gdal merge file size

Jeff Ruby jgr007 at gmail.com
Mon Dec 29 15:50:50 EST 2008

Hi Adam,

One of the quickest methods I've found for operations like this is to:

- use djpeg convert the images to pnm
- use pnmcat to concatenate images in the same row
- use pnmcat again to concatenate the rows
- use gdal_translate to convert the pnm to an unregistered tiff
- rename .jgw for upper left to appropriate .tfw

At that point you have a registered tif and you can use gdal_translate
to convert it to any image GDAL supports.

This method is a little clunky, but it's pretty fast.  If the image is
small enough you may be able to convert the pnm directly to jpg using

If you're using Windows djpeg/cjpeg and pnmcat all work well through
cygwin for this purpose.  I've used it to create tiffs that are on the
order of 100GB.

If anyone has another method, I'd love to hear it.


On Mon, Dec 29, 2008 at 2:45 PM, Adam Yesaitis <adamy at wtgroupllc.com> wrote:
> Hello,
>     I am attempting to use the gdal_merge utility to mosaic pre-registered
> aerial photographs and provide a worldfile for the output.  I am using RGB
> satellite images in .JPG format averaging about 7MB per image.  The problem
> is that my output file size for say 10 images is extremely large ( 5.9
> GB).  Also it takes a very long tome for the utility to complete with only
> 10 maps.  Is there anything I can do to drastically reduce the size of my
> output to better reflect the initial input sizes or any way I can speed the
> process up?  Any thoughts would be greatly appreciated.
> Adam Yesaitis
> Western Technologies Group
> Tel: 908-725-1143
> Fax: 908-725-1488
> E-mail: adamy at wtgroupllc.com
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