[mapserver-users] Rasters

[Frank Warmerdam]

On 11-06-16 06:37 AM, afarrell wrote:
> Hi,
>
> I've converted some 8 bit rasters to GeoTIFF format and spherical mercator
> projection using FME.
> I'm getting large blue edges where the tiles meet:
>
> http://dl.dropbox.com/u/23077047/Misc1use/rasters.jpg
> http://dl.dropbox.com/u/23077047/Misc1use/rasters.jpg
>
> In ArcGIS the tiles appear seamless.
>
> Is this because MapServer do not support the nodata tiff tag, as it is not
> officially part of the geotiff standard
> (http://www.awaresystems.be/imaging/tiff/tifftags/gdal_nodata.html). I
> do not believe there is a problem with the files we are writing, as other
> applications (e.g. ArcCatalog) pick up on the nodata value just fine.

Annette,

I would be interested in seeing a gdalinfo report on one of the
GeoTIFF files produced with FME.  The problem isn't that the
tag is non-standard (after all it is a GDAL produced tag and
MapServer uses GDAL as does FME and ArcGIS).  The problem is
just in the MapServer raster layer implementation and whether it
honours the metadata.

An immediate work around is to figure out what that blue pixel
value is and set the OFFSITE keyword in your raster layer to
match it.

For instance if the blue were red=0, green=149, blue=189 you
would add the following in the LAYER:

   OFFSITE 0 149 189

Ideally though, MapServer would pick it up automatically.

> Another potential solution is to add an alpha band to the raster instead of
> a nodata value. Do you think MapServer will support this?

yes

> Would using ecw images resolve the issue?

no, and it is often very difficult to keep track of nodata
areas in lossily compressed formats like ecw, mrsid, jpeg2000
and jpeg.



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