DGIWG Geodetic Codes and Parameters Registry
All Spatial Data must be referenced to a coordinate system. Geographic Information on the earth must be referenced to a Coordinate Reference System (CRS) based on a set of Geodetic Parameters. ISO standard 19111:2007 defines the conceptual schema for the description of spatial referencing by coordinates.
In order to combine or use multiple data sources together they must make use of the same CRS. In some situations transformations are required between CRSs to convert data.
In order to simplify the the integration of data DGIWG makes use of only one CRS for data production. This CRS is the World Geodetic System 1984 (WGS 84).
Imagery and paper map products must be projected and the projection transform adds an additional complication for the integration of data, where projection transforms are also required. Several different projections are used to define grid systems in different raster data products. One has been defined through DGIWG called the The Equal Arc-Second Raster Chart/Map system, more usually known as the ARC System. (see DIGEST Support Document 3 - The ARC System).
Historically there are many different coordinate reference systems that have been used in various source data products. Even if this data is converted to WGS84 CRS it is still necessary to record the source coordinate reference system, and for projected data the source projection in the source metadata, and optionally the conversion process in the lineage metadata associated with the data set. As such there is a requirement to maintain a list of coordinate reference systems for use in metadata.
DGIWG maintains this list in a multi-part Geodetic Codes and Parameters Registry. It should be noted that this list is not a compliant description of CRS in alignment with ISO 19111. The register is based on the content of the older DIGEST 2.1 standard (part 3 section 6) and is intended for recording metadata as read from the legends of source maps and other source data products.
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