WCS GeoTIFF output and NaN _FillValue

[pacioos]

Hi THREDDS folks,
When downloading a GeoTIFF file using the Web Coverage Service (WCS) in our THREDDS Data Server (TDS), it does not set our _FillValue attribute to NoData in the resulting GeoTIFF file when the _FillValue is "NaN". When running gdalinfo on the downloaded GeoTIFF file (using GeoTIFF_Float as the output format), I see the following error message:

Warning 1: TIFFFetchNormalTag:Incompatible type for "GDALNoDataValue"; tag ignored

Perhaps the TDS WCS output is setting NaN as a string instead of defining it as a float? Here is an example dataset to test this with:

http:https://oos.soest.hawaii.edu/thredds/idd/bathymetry.html?dataset=ngdc_bathy_10m_tutuila

Here is an example WCS request using the above dataset to download a GeoTIFF of the full dataset at its native resolution:

http:https://oos.soest.hawaii.edu/thredds/wcs/ngdc_bathy_10m_tutuila?service=WCS&version=1.0.0&request=GetCoverage&coverage=elev&format=GeoTIFF_Float&bbox=-170.95,-14.4,-170.44999,-14.18&resx=0.0000925942&resy=0.0000925942

Without NoData defined, the resulting GeoTIFF gets filled in over land (the island of Tutuila in American Samoa) even though this bathymetry dataset only covers the surrounding ocean.
Thanks,
John Maurer
Data System Engineer
Pacific Islands Ocean Observing System (PacIOOS)
University of Hawaii at Manoa