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The global attribute "Conventions" must be specified in the netcdf file (e.g. Conventions="CF-1.6"). If this attribute is not present or not valid, then the NetCDF Java library assumes a default convention (different from CF), which can cause unexpected behaviour in the NetCDF import in Delft-FEWS. Also see http://cfconventions.org/Data/cf-conventions/cf-conventions-1.6/build/cf-conventions.html#identification-of-conventions.
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Gridded data
See for references to the cf-conventions website below.
- all variables (data and coordinate) must have a unique variable name and the following attributes:
- units (required, see units link below)
- standard_name (required, see standard_name link below) - should comply with standard names list
- long_name (recommended, see long_name links below)
- _FillValue and/or missing_value (required if data contains missing values)
- scale_factor (optional to compact data)
- add_offset (optional to compact data)
see cf-conventions on these:
units http://cfconventions.org/Data/cf-conventions/cf-conventions-1.6/build/cf-conventions.html#units,
standard-name http://cfconventions.org/Data/cf-conventions/cf-conventions-1.6/build/cf-conventions.html#standard-name
http://cfconventions.org/Data/cf-standard-names/26/build/cf-standard-name-table.html
long-name http://cfconventions.org/Data/cf-conventions/cf-conventions-1.6/build/cf-conventions.html#long-name
- Data variable for a 2D grid must depend on three dimensions, representing time and two spatial dimensions (in either the order time, y, x or time, x, y). The names of the dimensions can be anything.
- regular or rectangular grids - each spatial dimension must have a corresponding 1D coordinate variable with the same name.
See http://cfconventions.org/Data/cf-conventions/cf-conventions-1.6/build/cf-conventions.html#idp5553648. - curvilinear grids - both spatial dimensions are 2D and depend on both spatial dimensions.
- Time coordinate variable requires axis "T"
- x coordinate variable requires axis "X"
- y coordinate variable requires axis "Y"
- (optional) analysis_time coordinate, see below
- The data variable must have an attribute "coordinates" that refers to the y and x coordinate variables (in that order), e.g. coordinates="y x". See http://cfconventions.org/Data/cf-conventions/cf-conventions-1.6/build/cf-conventions.html#idp5559280.
- Each coordinate variable must have an attribute "axis" that indicates which axis is defined by that coordinate variable.
- Time dimension must have a corresponding 1D time coordinate variable with the same name.
- Spatial dimensions, for
- regular or rectangular grids - each spatial dimension must have a corresponding 1D coordinate variable with the same name.
- Time coordinate variable must have the attributes
- "units" with a valid unit of time - e.g. units="minutes since 1970-01-01 00:00:00.0 +0000"
See http://cfconventions.org/Data/cf-conventions/cf-conventions-1.6/build/cf-conventions.html#time-coordinate - "axis" with value "T"
- "units" with a valid unit of time - e.g. units="minutes since 1970-01-01 00:00:00.0 +0000"
- Forecast reference time/analysis time/base time (optional), must be stored in a separate coordinate variable that
- contains only one value: the forecast reference time, and
- standard_name="forecast_reference_time"
The name of this variable must be present in the coordinates attribute of the data variable, e.g. coordinates="analysis_time" or coordinates="y x analysis_time".
If needed, different data variables can point to different forecast reference time variables.
See http://cfconventions.org/Data/cf-conventions/cf-conventions-1.6/build/cf-conventions.html#scalar-coordinate-variables
- Time and spatial coordinate variables must have values either in ascending or in descending order.
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- Data variable for a 2D grid must depend on three dimensions, representing time and two spatial dimensions (in either the order time, y, x or time, x, y). The names of the dimensions can be anything.
- Time dimension must have a corresponding 1D time coordinate variable with the same name.
- Spatial dimensions, for
- regular or rectangular grids - each spatial dimension must have a corresponding 1D coordinate variable with the same name (see coordinates link below).
- curvilinear grids - both spatial dimensions are 2D and depend on both spatial dimensions.
- The data variable must have an attribute "coordinates" that refers to the y and x coordinate variables (in that order), e.g. coordinates="y x"
- Each coordinate variable must have an attribute "axis" that indicates which axis is defined by that coordinate variable.
- Time coordinate variable requires axis "T"
- x coordinate variable requires axis "X"
- y coordinate variable requires axis "Y"
- (optional) analysis_time coordinate, see below
- Time coordinate variable must have the attributes
- "units" with a valid unit of time - e.g. units="minutes since 1970-01-01 00:00:00.0 +0000" (time coordinate link below)
- "axis" with value "T"
- Time and spatial coordinate variables must have values either in ascending or in descending order.
- Forecast reference time/analysis time/base time (optional), must be stored in a separate coordinate variable that
- contains only one value: the forecast reference time, and
- standard_name="forecast_reference_time"
The name of this variable must be present in the coordinates attribute of the data variable, e.g. coordinates="analysis_time" or coordinates="y x analysis_time".
If needed, different data variables can point to different forecast reference time variables (see scalar coordinate link below).
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Topic | Link to cfconventions.org |
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units | http://cfconventions.org/Data/cf-conventions/cf-conventions-1.6/build/cf-conventions.html#units |
standard_name |
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.6/build/cf-conventions.html#standard-name http://cfconventions.org/Data/cf-standard-names/26/build/cf- |
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standard-name-table.html | |
long_name | http://cfconventions.org/Data/cf-conventions/cf-conventions-1.6/build/cf-conventions.html#long-name |
regular grids Lat, Long, Vert, and Time Axes | http://cfconventions.org/Data/cf-conventions/cf-conventions-1.6/build/cf-conventions.html#idp5553648 |
coordinates |
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Compacted data
Netcf data variables with attributes scale_factor and add_offset will be treated as compacted data and the values of these attributes will be used to uncompact the values of this variable.
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