[Gdal-dev] Black border (null value) after changing projection: possible to remove this?

[Vincent Schut]

-------- Original Message --------
From: wqual <wolfgang.qual at gmx.net>
To: gdal-dev at lists.maptools.org
Subject: [Gdal-dev] Black border (null value) after changing
projection:    possible to remove this?
Date: 07/19/2006 09:27 AM
> Hi gdal-list,
> Recently, I had to change the projection of some satellite tiles. I used 
> gdalwarp for this purpose and it worked perfectly. 
> The only thing is: as the tiles were rotated a little bit, black triangles 
> (representing null-values) appear because of the rotation).
> When I load these tiles in one view or a mapserver map, these black triangles 
> overlay adjacent tiles a little bit. 
> Therefore my question:
> Is there a possiblity to remove these "triangles" resp.: can I define them as 
> transparent? I would like to put them into a mapserver map using gdaltindex.
>
> I would be grateful for some comments about this.
>   
You can do this in mapserver by defining an OFFSITE <rgb color>
parameter in your raster layers in your mapfile. This works as long as
those triangles are really constant of color, or in other words: they'd
better not be jpegs because the jpeg compression will add noise to your
nice black areas. We've been using this trick extensively to overlay
raster imagery (landsat scenes, etc) on other data using mapserver,
including raster on raster. It works perfectly. See the mapserver
mapfile documentation (layer object, offsite parameter) for more info.

Regards,
Vincent.
> Best regards,
> Wolfgang
>
>
>
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