[Geotiff] C API for unofficial private tags GDAL_NODATA and GDAL_METADATA

[Pierre Soille]

Hello,

when writing GeoTIFF files from a C programme using libgeotiff API, I
would like to include the unofficial private tags GDAL_NODATA and
GDAL_METADATA.  However, so far I did not succeed doing this for it
seems that they are not defined in the current header files associated
with libgeotiff-1.4.0.   Any hint would be very much appreciated.

Best regards,

Pierre Soille