[gdal-dev] Mosaicking Orthos

Zoltan Szecsei zoltans at geograph.co.za
Wed Feb 16 06:55:53 EST 2011


On 2011-02-16 12:20, Zoltan Szecsei wrote:
> Hi All,
> I've built a vrt with 176 images.
>
> I now need to mosaic this whole area into roughly 5 x 5 ortho images.
>
> How can I force the white edges into background of the overlapping 
> orthos?
> I'm a little cautious of simply (finding a way to) making "white" 
> transparent as it is only the white on the edges that need to be 
> backgrounded.

Hi again,
Since the above post, I have tried different ways to set nodata, but to 
no avail - I still get the white edges:
(see jpeg sent with my original post)

gdalbuildvrt -addalpha -hidenodata -input_file_list files 
177_untiled_orthos_nodata.vrt
gdalbuildvrt -srcnodata "0 0 0"  -addalpha -hidenodata -input_file_list 
files 177_untiled_orthos_blk.vrt
gdalbuildvrt -srcnodata "255 255 255"  -addalpha -hidenodata 
-input_file_list files 177_untiled_orthos_white.vrt

How should I be masking out the nodata (or even white pixels) so that 
when I mosaic a bunch of tiffs together, I dont get the white stripes in 
the resulting image?

Using GDAL 1.7.3, released 2010/11/10 on Ubuntu 10.04
Viewing with Quantum GIS - 1.6.0-Trunk on Ubuntu 10.04 (same box).
...but running the whole lot in xterms with Xming & putty from my 
WinVista box.


Regards,
Zoltan




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Zoltan Szecsei PrGISc [PGP0031]
Geograph (Pty) Ltd.
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