The NetCDF Markup Language (NcML) version 2.1
NcML Core
NcML OBJECT MODEL
An abstract object model for expressing metadata associated with generic netCDF data
specification , UML diagram
NcML SCHEMA
A schema in XSD format following the netCDF Metadata Object Model (release 1.0):
Examples:
NcML METADATA EXTRACTION
The NCAR community portal has a prototype web application for the extraction of NcML metadata from any network-retrievable netcdf file.
NcML Coordinate System
NcML Coordinate System extends the netCDF data model to add explicit support for general and georeferencing coordinate systems. The ucar.nc2.dataset package in the NetCDF Java library, version 2.1 implements the object model, creating a subclass of NetcdfFile called NetcdfDataset. The ucar.nc2.dataset.conv package adds a framework for parsing Conventions to extract the coordinate systems and turn a NetcdfFile into a NetcdfDataset. NcML Coordinate System is essentially the external XML representation of that extended netCDF data model.
Summary of extensions to Core:
- netcdf is redefined to allow coordinateSystem and coordinateTransform elements.
- variable is redefined to allow the coordinateSystems attribute, which lists the coordinate systems for this variable.
- coordinateAxis extends variable, adding the units attribute, as well as optional attributes axisType, positive and boundaryRef
- axisType attribute identifies georeferencing coordinate axes. It has the possible values of GeoX, GeoY, GeoZ, Height, Pressure, Lat, Lon, or Time.
- positive attribute is only used for vertical coordinate axes, and gives the direction of increasing values. It has the value up or down.
- boundaryRef attribute is the name of a variable that is the boundary of this coordinate axis.
- coordinateSystem is a list of coordinateAxis elements, and optional coordinateTransform elements.
- coordinateTransform represents a mathematical transformation of one coordinate system to another. It has a list of name/value pairs, called parameters, and an optional transformType that has the value Projection or Sigma.
An annotated schema in HTML.
The latest NcML Coordinate System schema in XML (release 1.0 beta).
Examples:
NcML Dataset
NcML Dataset allows you to use NcML to define a netCDF file, similar to the ncgen command line tool, as well as to redefine, aggregate, and subset existing netCDF files.
Summary of extensions to Core:
- netcdf is extended to allow readMetadata, aggregation and nested netcdf elements.
- variable is extended to allow the nameInFile attribute, which allows you to rename a variable, and the logicalView element, which allows you to specify the data as a subset of another variable.
- readMetada allows you to read all or some of the variables, attributes and dimensions from another netCDF dataset, as well as rename them.
- aggregation allows you to aggregate variables from nested netcdf elements into a single logical variable.
- values is extended to allow the definition of regularly spaced values using a start and increment.
We are on version 2 of this specification:
Previous version:
