[Gdal-dev] Help With Transparent Colors

[Reinaldo Escada Chohfi]

You can also use the GeoExpress 5.0 trial download from LizardTech 
(www.lizardtech.com) that allows you to mosaic and reproject .sid images in 
one step.  The trial download allows you to work with images that already 
are in .sid format without problems.  That way you don't need to go from 
MrSID to GeoTiff and make a large mosaic as a .sid image.

Best regards,

Reinaldo

At 09:06 PM 1/24/2006, Frank Warmerdam wrote:
>On 1/24/06, Dolloff, Matthew D. (JSC-ER7) <matthew.d.dolloff at nasa.gov> wrote:
> >
> >
> >
> > Hello.  I am trying to convert some MrSID images into Geotiffs and tiling
> > them together.  The MrSIDs are in state plane coordinate system and I need
> > them in WGS84.  So I convert the MrSIDs to geotiffs using mrsiddecode from
> > lizard tech.  Then I use gdal warp to change the projection type.  Then use
> > gdal_merge to merge them together.  The problem is that I end up with a
> > black collar when I warp the images and then when I merge them the images
> > cover each other up.  Is there anyway, that I can crop those collars out?
> > Here is the link where I am getting the sids
> > 
> http://www.nysgis.state.ny.us/gateway/mg/2001/suffolk/01ic_t_babylon_l06col.htm
>
>Matt,
>
>A couple of approaches would be:
>
>  o Use gdal_merge to merge the TIFFs before
>     reprojecting them.  Then gdalwarp the resulting
>     mosaic.
>
>  o Or create a big WGS84 mosaic file and gdalwarp
>     each non-WGS84 file into that, mosaicing at the
>     same time as reprojecting.
>
>In the future gdalwarp will support multiple input
>files, essentially replacing gdal_merge for many
>purposes.  This is already in CVS if you were building
>from source.  Another option would be to generate a
>nodata value or better yet an alpha channel in the files
>output by gdalwarp to keep track of the nodata pixels.
>
>My suggestion would be the top most option, mosaic
>then reproject.  Keep in mind that GeoTIFF only
>supports file sizes up to 4GB.  So if your mosaic is
>going to be large, you may need to do it in a format
>like Erdas Imagine.
>
>Best regards,
>--
>---------------------------------------+--------------------------------------
>I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam at pobox.com
>light and sound - activate the windows | http://pobox.com/~warmerdam
>and watch the world go round - Rush    | Geospatial Programmer for Rent
>
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Reinaldo Escada Chohfi, Ph.D.
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