Grids and Beyond: netCDF-CF and ISO/OGC Features and Coverages

Ethan Davis, John Caron, Ben DomenicoUCAR/Unidata

AMS IIPS, 23 January 2008

Non-gridded Data

Modeling Scientific Datatypes• Point, Station, Profile, Trajectory, Grid, …

– Unidata CDM– CSML– OGC O&M

• Why– Categorize by structure/connectedness– Consider specialized queries in space and time– Help with encoding (netCDF, CF)

• How– ISO Coverage model (ISO 19123)

Why ISO Coverages?

• Very general model for representing fields that vary over a spatial domain (e.g., temperature)

• Promote interoperability– Well accepted standard

• OGC WCS data access protocol is based on the ISO Coverages

OGC Web Coverage Service

• Specification for accessing subsets of gridded data.

• Currently restricted to gridded data and further to regularly spaced gridded data.

• Not due to limitations of the ISO coverage model.

WCS and Non-gridded Data

• Possible?• What is needed

– Model datatypes using ISO Coverage model– Translate the model to XML/GML– WCS response encodings (netCDF-CF)– WCS queries

ISO Coverage and Feature

• ISO coverage is an extension of the ISO feature concept

• Feature is an abstract representation of a real-world phenomena.

• A bit more concretely …

ISO Coverage and Feature

Simple Feature: generally an object with some spatial extent or geometry and a set of attributes. E.g., a lake has a shoreline and a name

ISO Coverage and Feature

Coverage: a spatial domain and the set of parameters that vary over that domain. E.g., a lake has a depth at every point.

ISO Coverage and Feature Different views of the same data

Collection of point features

Time series coverage

WCS and Non-gridded Data

• Possible?• What is needed

– Model datatypes using ISO Coverage model– Translate the model to XML/GML– WCS response encodings (netCDF-CF)– WCS queries

WCS and Non-gridded Data

• Possible?• What is needed

– Model datatypes using ISO Coverage model– Translate the model to XML/GML– WCS response encodings (netCDF-CF)– WCS queries

WCS and Non-gridded Data

• Possible?• What is needed

– Model datatypes using ISO Coverage model– Translate the model to XML/GML– WCS response encodings (netCDF-CF)– WCS queries

WCS Response EncodingnetCDF-CF

• netCDF-CF good for gridded data– Including irregularly spaced grids– Non-gridded not as fully specified

• Current efforts to extend CF– Unidata Point Observation Convention– Coordinate Reference System (CRS)

proposal– Unstructured grids

WCS and Non-gridded Data

• Possible?• What is needed

– Model datatypes using ISO Coverage model– Translate the model to XML/GML– WCS response encodings (netCDF-CF)– WCS queries

WCS Queries

• Current WCS queries:– Lat/lon/Z (X/Y/Z) bounding box– Time range– Parameter selection (subsettable if there is a

parameter dimension, e.g., spectral bands)• What other queries would be useful with

non-gridded data

WCS Queries

Specialized queries for a datatype..

Example: Station collection

Request:bbox=10,-105,50,-80

WCS Queries

Specialized queries for a datatype..

Example: Station collection

WCS Queries

Specialized queries for a datatype..

Example: Station collection

Request:Stn=71815,71867,72214

WCS Queries

Extract one datatype from another datatype.

Example: Time series from a grid at a given point.

Request:datatype=timeseries&pnt=30,-90

WCS Queries

Extract one datatype from another datatype.

Example: Vertical profile from a 3-D grid at a given point.

Request:datatype=profile&pnt=30,-90

WCS Queries

Extract one datatype from another datatype.

Example: Trajectory data from a 4-D grid, given an xyzt curve.

Request:datatype=trajectory& ???

WCS Queries

Extract one datatype from another datatype.

Example: Trajectory data from a 4-D grid, given an xyzt curve.

Request:datatype=trajectory &featureURI=flightTrack.xml

WCS Queries

Extract one datatype from another datatype.

Example: Station data from a grid.

Request:datatype=station& ???

WCS Queries

Extract one datatype from another datatype.

Example: Station data from a grid.

Request:datatype=station &featureURI=stnList.xml

WCS and Non-gridded Data

• Possible?• What is needed

– Model datatypes using ISO Coverage model– Translate the model to XML/GML– WCS response encodings (netCDF-CF)– WCS queries

WCS and Non-gridded Data

• Possible?• What is needed

– Model datatypes using ISO Coverage model– Translate the model to XML/GML– WCS response encodings (netCDF-CF)– WCS queries– Evolve the WCS specification

Thanks

• BADC (Andrew Woolf, Bryan Lawrence)• UK Met Office (Jeremy Tandy, Bruce Wright)• Univ of Florence (Stefano Nativi)• CSIRO (Simon Cox)• OGC• GALEON

Contacts

Ethan Davis, edavis@unidata.ucar.edu