[gdal-dev] Need some info on geotiff tags missing

[Even Rouault]

Le samedi 02 août 2014 23:48:54, Andrea Peri a écrit :
> Hi,
> 
> I have transform many old tiff+tfw rasters using this gdal transformation:
> 
> gdal_translate -ot Byte -of GTiff -b 1 -a_nodata none -stats -co
> COMPRESS=NONE -co INTERLEAVE=PIXEL -co PROFILE=GDALGeoTIFF -co
> TILED=YES -co BLOCKXSIZE=256 -co BLOCKYSIZE=256 -co SPARSE_OK=TRUE -co
> TFW=NO filein.tif fileout.tif
> 
> They are wrking correctly with qgis and with mapserver for several months.
> 
> Now I need to use this geotiffs with another program.
> But this program say that these images are not realy GeoTiffs.
> 
> I test them using listgeos and have this result:
> 
> TIFFReadDirectory: Warning, Unknown field with tag 42112 (0xa480)
> encountered. Geotiff_Information:
>    Version: 1
>    Key_Revision: 1.0
>    Tagged_Information:
>       ModelTiepointTag (2,3):
>          0                0                0
>          559417.445637    4927786.430528   0
>       ModelPixelScaleTag (1,3):
>          0.5              0.5              0
>       End_Of_Tags.
>    Keyed_Information:
>       End_Of_Keys.
>    End_Of_Geotiff.
> 
> Some people say me that this is not a true geotiff because are missing
> several tags.
> I reported a supposed response from a real geotiff:
> 
> Geotiff_Information:
>     Version: 1
>     Key_Revision: 1.0
>     Tagged_Information:
>        ModelTiepointTag (2,3):
>           0                 0                 0
>           673347            4298291           0
>        ModelPixelScaleTag (1,3):
>           1                 1                 1
>        End_Of_Tags.
>     Keyed_Information:
>        GTModelTypeGeoKey (Short,1): ModelTypeProjected
>        GTRasterTypeGeoKey (Short,1): RasterPixelIsArea
>        GTCitationGeoKey (Ascii,37): "NAIP 2012
> m_3808409_sw_16_1_20120607"
>        ProjectedCSTypeGeoKey (Short,1): PCS_NAD83_UTM_zone_16N
>        PCSCitationGeoKey (Ascii,21): "NAD83 / UTM zone 16N"
>        ProjLinearUnitsGeoKey (Short,1): Linear_Meter
>        End_Of_Keys.
>     End_Of_Geotiff.
> 
> PCS = 26916 (NAD83 / UTM zone 16N)
> Projection = 16016 (UTM zone 16N)
> Projection Method: CT_TransverseMercator
>     ProjNatOriginLatGeoKey: 0.000000 (  0d 0' 0.00"N)
>     ProjNatOriginLongGeoKey: -87.000000 ( 87d 0' 0.00"W)
>     ProjScaleAtNatOriginGeoKey: 0.999600
>     ProjFalseEastingGeoKey: 500000.000000 m
>     ProjFalseNorthingGeoKey: 0.000000 m
> GCS: 4269/NAD83
> Datum: 6269/North American Datum 1983
> Ellipsoid: 7019/GRS 1980 (6378137.00,6356752.31)
> Prime Meridian: 8901/Greenwich (0.000000/  0d 0' 0.00"E)
> Projection Linear Units: 9001/metre (1.000000m)
> 
> Corner Coordinates:
> Upper Left    (  673347.000, 4298291.000)  ( 85d 0'12.06"W,
> 38d48'58.87"N)
> Lower Left    (  673347.000, 4290632.000)  ( 85d 0'18.99"W,
> 38d44'50.54"N)
> Upper Right   (  679532.000, 4298291.000)  ( 84d55'55.75"W,
> 38d48'54.41"N)
> Lower Right   (  679532.000, 4290632.000)  ( 84d56' 2.92"W,
> 38d44'46.10"N)
> Center        (  676439.500, 4294461.500)  ( 84d58' 7.43"W,
> 38d46'52.50"N)
> 
> -----
> 
> I'm a bit confused.
> Because I have produced my GeoTiffs using gdal. And if it fail to
> produce a real geotiff I have a trouble.
> 
> So the main question is a geotiff ith only the tags reported a real geotiff
> ?

Andrea,

The difference between the 2 geotiff is that the first one does not have 
information on the spatial reference system, but only the geotransform that 
comes from the .tfw file.
Skimming quickly through the GeoTIFF specification ( 
http://www.remotesensing.org/geotiff/spec/contents.html ) doesn't immediately 
show if it is valid or not, although it would be best if readers are robust to 
missing information.
If you know the SRS of the maps, you can try adding -a_srs EPSG:XXXX or -a_srs 
wkt_string.
You could also try -a_srs "LOCAL_CS[\"Unknown\"]" if you don't know the SRS at 
all. This will write a few geotiff keys to define a unknown CRS, but it is not 
obvious that your reader will like it.

Even

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