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Welcome to the CRSdefinitionResolver web

Preface

OGC provides a resolver for various types of definitions, such as Coordinate Reference Systems (CRSs), coordinate axes, units of measure, etc., identified by a URI (NB: OGC uses URLs). The task of a resolver is, when receiving a URL identifying a concept, to return its definition. Typically this will be in a GML encoding, but other representations might be provided at some time, too.

Generally, such definitions sit in the def/ branch of OGC's name type system. CRSs and axes are gathered in def/crs/ and def/axis/, respectively.

There is a wide and growing range of CRS definitions maintained. As OGC’s mission centers around location-based data and services, practically all OGC specifications make heavy use of CRSs to relate object locations in space and time to some reference position. A vast amount of different definitions is in practical use, covering horizontal (geodetic) extents, height, and time. New definitions arise, such as in planetary sciences.

CRS handling follows the OGC CRS Name Type Specification (OGC 11-135): "This OGC Best Practice document defines a syntax, based on http URIs, for identifying Coordinate Reference Systems (CRSs), including compound and parameterized CRSs. Strings conforming to this syntax are called CRS URIs. The semantics of such definitions is established by the OGC registry service. The specification on hand does not define concrete URIs, it only establishes an URI scheme; definition of CRS URIs based on this scheme, such as temporal CRSs, is done separately within OGC."

Technology

The def/crs and def/axis branches are maintained by SECORE, the open-source resolver implementation of rasdaman. All other branches are maintained by CSIRO.

Discussion

Generally, speaking, n-D CRS handling is a young, very dynamic field. Therefore, sometimes new requirements come in from stakeholders. This section gathers such items.

Case Sensitivity

Simon Cox: I just discovered that the URI redirects associated with EPSG CRS parameters are case-sensitive, so generate different responses: the former goes to SECORE, and the latter to the EPSG Indicio registry. This clearly is undesirable. They should go to the same place, and that place should be SECORE.

(This problem seems solved now) -- PieroCampalani - 25 Nov 2013

The redirection mechanism is currently not working as expected and it seems that only EPSG related definitions actually redirected to SECORE:

  1. http://www.opengis.net/def/axis/OGC/1.0/East
  2. http://www.opengis.net/def/crs/
  3. http://www.opengis.net/def/crs/OGC/
  4. http://www.opengis.net/def/crs/<authority!EPSG>;
  5. ...

-- PieroCampalani - 25 Nov 2013

Index CRSs

Additionally to geospatial EPSG CRSs, the CRS resolver will manage other authorities (as for any other OGC definition). Work is under process to submit new OGC resources identifiers for non-spatial CRSs, like for temporal definitions (see Temporal DWG wiki) and Index CRS, to act as generalization to nD of the currently available Image CRS definition: instead of being anchored to a 2D image, these CRSs will anchor to an n-dimensional array of contiguous cells.

Parametrized CRS types offer the chance to keep a simple and clean code, while letting a customization of the CRS definition via KV-pairs (e.g. the datum to be in the centre of nD cell by default, but with a parametrizable offset). This can avoid overly long codes like what happened for previous identifiers for Image CRSs: http://www.opengis.net/def/crs/OGC/1.0/ImageCRSpixelCorner, etc.

For a preview of the definitions, see:

-- PieroCampalani - 25 Nov 2013

CRSdefinitionResolver Web Utilities

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Topic revision: r3 - 25 Nov 2013, PieroCampalani
 

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