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20011108: using 9999 as a missing data value

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  • Subject: 20011108: using 9999 as a missing data value
  • Date: Thu, 08 Nov 2001 07:40:11 -0700
>From: "M.R.SRIDHAR" <address@hidden>
>Organization: ?
>Keywords: 200111080515.fA85F6124645 netcdf missing value

Sridhar,

>i am sridhar working on oceandata modelling..i  have one ascii file
>which consists of latitude,longitude,sealevel,julianday,date,month
>,year. The latitude and longitude is of .25 gridded...in sealevel there
>are few missing data (9999) available in the ascii file...when i am
>putting the values into netcdf format for the sealevel which is the
>function of lat,long and time. I want to know whether in the place of
>missing value whether i should put 9999 or blank...

netCDF allows you to define what the missing data value is.  If you are
not doing this (as an attribute to the variable you are defining), then
the program that eventually reads the file will not know what particular
value is supposed to be interpreted as a missing value.  You can also
define the valid range of a variable.  Values outside of that
range _should_ be treated as bad, but that will be up to the application
reading the netCDF.

>i could able to put
>9999 but when the .nc file visualised through ferret its not reading
>properly and giving junk plots.So i am requesting you to give solution
>for this.

It doesn't sound like you defined a missing value for your netCDF file.
When doing so, remember that the missing value will be of the same type
as the variable.  So, if your latitudes and longitudes are floats;
the missing value will be a float; if the values are doubles, then
the missing value will be a double; etc.  Please check the netCDF
User's Guide form more information on how to define variable
attributes.

One last small comment.  A lot of people use -9999 as missing data
values, but, again, you are free to choose a value that does not lie
in th valid range of the variable in question.

>Thanking you

Good luck!

>Regards
>Sridhar.M.R. 

Tom Yoksas