Unidata - To provide the data services, tools, and cyberinfrastructure leadership that advance Earth system science, enhance educational opportunities, and broaden participation. Unidata
         
  advanced  
 

Next: , Previous: Unlimited Dimensions, Up: Intro


1.5 Fill Values

Sometimes there are missing values in the data, and some value is needed to represent them.

For example, what value do you put in a sea-surface temperature variable for points over land?

In netCDF, you can create an attribute for the variable (and of the same type as the variable) called “_FillValue” that contains a value that you have used for missing data. Applications that read the data file can use this to know how to represent these values.

Using attributes it is possible to capture metadata that would otherwise be separated from the data. Various conventions have been established. By using a set of conventions, a data producer is more likely to produce files that can be easily shared within the research community, and that contain enough details to be useful as a long-term archive.

For more information on _FillValue and other attribute conventions, see Attribute Conventions.

Climate and meteorological users are urged to follow the Climate and Forecast (CF) metadata conventions when producing data files. For more information about the CF conventions, see http://cf-pcmdi.llnl.gov.

For information about creating attributes, see Creation.
 
 
  Contact Us     Site Map     Search     Terms and Conditions     Privacy Policy     Participation Policy
 
National Science Foundation (NSF) UCAR Office of Programs University Corporation for Atmospheric Research (UCAR)   Unidata is a member of the UCAR Office of Programs, is managed by the University Corporation for Atmospheric Research, and is sponsored by the National Science Foundation.
P.O. Box 3000     Boulder, CO 80307-3000 USA     Tel: 303-497-8643     Fax: 303-497-8690