2008.09.23 16:57 "Re: [Tiff] New to list, with a query on TIFFTAG_GDAL_METADATA", by Frank Warmerdam

I'm new to this list, so please forgive any netiquette errors!

I have a GeoTIFF application working with FWTools V1.3.7 DLLs, and using Delphi as my language. I now need to write some GDAL data, so I woudl like to do something like this:

  TIFFSetField (tif, TIFFTAG_GDAL_METADATA, PChar (txt));

However, the field is unrecognised, and trying to define a new TIFF field using

TIFFMergeFieldInfo seems to be complicated and indeed to be deprecated. How should I be doing this?

David,

GDAL uses this code to merge in the TIFFTAG_GDAL_METADATA tag.

static void GTiffTagExtender(TIFF *tif)

{
     static const TIFFFieldInfo xtiffFieldInfo[] = {

         { TIFFTAG_GDAL_METADATA,    -1,-1, TIFF_ASCII, FIELD_CUSTOM,
           TRUE,        FALSE,  (char*) "GDALMetadata" },
         { TIFFTAG_GDAL_NODATA,     -1,-1, TIFF_ASCII,  FIELD_CUSTOM,
           TRUE,        FALSE,  (char*) "GDALNoDataValue" },
         { TIFFTAG_RPCCOEFFICIENT,   -1,-1, TIFF_DOUBLE,        FIELD_CUSTOM,
           TRUE,        TRUE,   (char*) "RPCCoefficient" }

     };

     if (_ParentExtender)
         (*_ParentExtender)(tif);

     TIFFMergeFieldInfo( tif, xtiffFieldInfo,
                        sizeof(xtiffFieldInfo) / sizeof(xtiffFieldInfo[0]) );
}

I'm not at all sure how this might be accomplished from Delphi Pascal.

Libtiff should automatically prepare a definition for the tag if it is encountered in an existing file, but I don't know how you would add such a tag to a new file without defining it.

I'm not aware of a newer cleaner way of doing the same thing.

Best regards,
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