THREDDS Web Coverage Service

The THREDDS WCS Server implements the OGC Web Coverage Service (WCS) 1.0.0 specification. It serves out gridded data in GeoTIFF or NetCDF format.

Status

The THREDDS WCS server is considered experimental, do not rely on it in a production environment.

Which files can be served through the WCS server?

  1. Data files must contain gridded data.
  2. The NetCDF-Java Common Data Model must be able to identify the coordinates system used. Check this by opening in the Grid Panel of the ToolsUI application. There should be one or more variables shown as a GeoGrid.
  3. Currently due to WCS and GeoTIFF limitations, the X,Y and (if it exists) Z axes must be regularly spaced.

Capabilities/Limitations

Current WCS 1.0.0 Implementation (version=1.0.0)

The current TDS implementation of WCS 1.0 has the following restrictions:

  1. No interpolation is available (i.e., interpolationMethod="none").
  2. CRS/SRS
    1. All CRS/SRS are listed as "WGS84(DD)" even though it may have little relation to the actual CRS of the data.
    2. CRS is horizontal, XY, only (see Range below for vertical, Z)
    3. The response coverage is in the native CRS of the data (as the "No Interpolation" item implies).
    4. The netCDF-Java library understands a number of projections (a subset of  the CF convention grid mapping options, and most assuming a spherical earth) including a simple lat/lon grid [-180/180 and -90/90].
    5. All BBOX requests are assumed to be in the lat/lon of the native projection.
  3. Temporal selection: only one value can be specified (no list or min/max/res).
  4. Range:
    1. Each coverage has only one range field
    2. "Vertical" is the range axis, only if the coordinate has a vertical component.
    3. Range axis selection: only one value can be specified (no list or min/max/res).
  5. Supported GetCoverage response formats:
    1. GeoTIFF: A grayscale 8-bit GeoTIFF file
    2. GeoTIFFfloat: A floating point "Data Sample" GeoTIFF file
    3. NetCDF3: A NetCDF file following the CF-1.0 convention

Upcoming WCS 1.0.0 Implementation (version=1.0.0.1)

Same as above (version=1.0.0) except:

  1. CRS/SRS
    1. Some improvment in CRS encoding (i.e., not all are listed as "WGS84(DD)")
  2. Temporal selection: only min/max is supported. No resolution is allowed on the min/max and no lists are allowed.
  3. "Vertical" range axis selection: only min/max is supported. No resolution is allowed on the min/max and no lists are allowed.
  4. Supported GetCoverage response formats:
    1. NetCDF3: A NetCDF file following the CF-1.0 convention
    2. GeoTIFF (Only supports requests for single time and single height.)
      1. GeoTIFF: A grayscale 8-bit GeoTIFF file
      2. GeoTIFF_Float: A floating point "Data Sample" GeoTIFF file

Upcoming WCS 1.0.0+ Implementation (version=1.0.0.11)

The WCS 1.0.0+ implementation experiment is targeted to further the understanding of how FES datasets fit into the current WCS and what extensions they may require. The conclusions will be fed back to the WCS 1.2 RWG.

As currently expected, same as above (version=1.0.0.1) except:

  1. CRS/SRS
    1. If coverage has vertical, it is part of the CRS
  2. Range:
    1. Each coverage can contain multiple range fields
    2. If range field is array, only min/max range axis selection allowed.
  3. Supported GetCoverage response formats:
    1. NetCDF3: A NetCDF file following the CF-1.0 convention
    2. GeoTIFF (Only supports requests for single time and single height.)
      1. GeoTIFF: A grayscale 8-bit GeoTIFF file
      2. GeoTIFF_Float: A floating point "Data Sample" GeoTIFF file

Configuration

 For datasets that can be served by WCS, all that is required is to reference a service with "WCS" as the service type and "/thredds/wcs/" as the value of the URL base. See the THREDDS WCS Configuration page for more details.

WCS Dataset URLs

All THREDDS WCS requests start with 

 http://servername:8080/thredds/wcs/

The next part of the path indicates which file to use 

 http://servername:8080/thredds/wcs/testwcs/sst.nc

This is typically the URL you will need to pass to a WCS client. The WCS Client then forms various queries to the THREDDS WCS server for that dataset, e.g.:

 http://servername:8080/thredds/wcs/test/sst.nc?request=GetCapabilities&version=1.0.0&service=WCS&

Examples

The following are WCS URLs for our test datasets:

Here are example WCS queries for the first dataset: 







This document is maintained by John Caron
and was last updated on Oct 08, 2007