[gdal-dev] Setting the noData flag in a GeoTIFF

[Even Rouault]

Selon Jonathan Moules <jonathanmoules at warwickshire.gov.uk>:

> Hi List,
>   I have a question about setting a value as "noData" in GeoTIFFs.
>
> I'm creating a Geotiff with this two stage process (mosaicing a lot of
> tiles together):
>
> gdalbuildvrt -hidenodata -srcnodata 255 -vrtnodata 255 -input_file_list
> >> tiff_list.txt 255.vrt
> >
> >
> >> gdal_translate -of GTiff -co TILED=YES -co BIGTIFF=YES -co COMPRESS=JPEG
> >>  -co JPEG_QUALITY=80 -co BLOCKXSIZE=512 -co BLOCKYSIZE=512 -co
> >> PHOTOMETRIC=YCBCR 255.vrt 255mask.tif
> >
> >
> The resultant image is fine, but when I access it, both via ArcGIS and QGIS
> it says that there is no noData value set.

Yes, and gdalinfo on 255mask.tif would report the same too. The reason is the
"-hidenodata" flag in the gdalbuildvrt. Remove it and it should work as
expected.

You don't need to rebuild your 255mask.tif. Just try :

python gdal_edit.py -a_nodata 255 255mask.tif (cf
http://www.gdal.org/gdal_edit.html)

>
> I've tried reading into it and came across this -
> http://www.gdal.org/frmt_gtiff.html - but it requires a deeper level of the
> GeoTIFF library than I have to make much sense of it.
>
> I did see "GDAL_TIFF_INTERNAL_MASK" and tried to set it to true (using -co
> and --config), but GDAL just complained about it not being a valid
> configuration option.

Masks are more unusual and difficult to master.

>
> Can GeoTiffs have a noData value in them that applications will see and
> honour? If so, can I set it in GDAL?
> It's not critically important, more nice-to-have and also trying to
> understand the format better
>
> Thanks,
> Jonathan
>
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