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Re: 20010531: ncgen Error when using _FillValue (fwd)

------- Forwarded Message

Date:    Thu, 31 May 2001 16:47:20 -0600
From:    Russ Rew <address@hidden>
To:      address@hidden
Subject: Re: 20010531: ncgen Error when using _FillValue 

>From: address@hidden
>Subject: ncgen Error when using _FillValue
>Organization: Weather.com
>Keywords: 200105312053.f4VKrDp24081 netCDF 3.4 _FillValue

Bill,

> Thanks, that was the trick.  Is this documented somewhere?  I hate
> to keep bugging you'll if it something I could have found myself.
> I checked the documentation and didn't really see a reference to it.

Yes, it's in Chapter 8 of the netCDF User's Guide for C, Fortran-77,
or Fortran-90, in the "_FillValue" entry of the table describing
Common Attributes:

  http://www.unidata.ucar.edu/packages/netcdf/guidec/guidec-13.html#HEADING13-0

where it says:

  ... If _FillValue is defined then it should be scalar and of the
  same type as the variable. ...

It's also not obvious that just using a real constant for an attribute
value in CDL implicitly declares the attribute to be of type double,
but that's in Chapter 10:

  http://www.unidata.ucar.edu/packages/netcdf/guidec/guidec-15.html#HEADING15-0

where it says:

  ... The data type of an attribute in CDL is derived from the type of
  the value assigned to it. ... 

  ... The form of a float constant is the same as a C floating-point
  constant with an 'f' or 'F' appended.

Another quicker resource you might try for finding answers to netCDF
questions is the search page that searches through replies to netCDF
support questions, linked at the bottom of the netCDF home page or
directly at:

  http://www.unidata.ucar.edu/glimpsedocs/ghnetcdf.html

For this question, you could type in the search query 

  _FillValue type mismatch

and in this case it returns 5 relevant replies to questions that
contained that phrase.

--Russ



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