Introduction

Introduction

The EPSG Geodetic Parameter Dataset, abbreviated to the EPSG Dataset, is a repository of parameters required to:

- define a coordinate reference system (CRS) which ensures that coordinates describe position unambiguously; 
- define transformations and conversions that allow coordinates to be changed from one CRS to another CRS. Transformations and conversions are collectively called coordinate operations.

The EPSG Dataset is maintained by IOGP. It conforms to ISO 19111:2019, Geographic information – Referencing by coordinates. It is distributed in three ways:

- the EPSG Registry, in full the EPSG Geodetic Parameter Registry, a web-based delivery platform with a graphic user interface (GUI) and an application programming interface (API). From this repository descriptions of CRSs and transformations may be output in well-known text (WKT) conformant to ISO 19162 or as GML documents.
- the EPSG Database, in full the EPSG Geodetic Parameter Database, an MS Access relational database with content derived from the online registry. 
- in a relational data model as SQL scripts which enable a user to create an Oracle, MySQL, PostgreSQL or other relational database and populate that database with the EPSG Dataset. 

The terms of use of the EPSG Dataset are available here.

IOGP Reports 373-07-01 through 373-07-06 form multi-part document for users of the EPSG Dataset.

- IOGP Report 373-07-01 (EPSG Guidance Note 7-1) – Understanding the EPSG Dataset, sets out detailed information about the Dataset content and its maintenance.
- IOGP Report 373-07-02 (EPSG Guidance Note 7-2) – Coordinate conversions and transformations including formulas, provides a detailed explanation of formulas necessary for executing coordinate conversions and transformations using the coordinate operation methods supported in the EPSG Dataset. Geodetic parameters in the EPSG Dataset are consistent with these formulas. 
- IOGP Report 373-07-03 (EPSG Guidance Note 7-3) – EPSG Registry API user guide (this document), is primarily intended to assist computer application developers who wish to use the RESTful API of the EPSG Registry to query and retrieve entities and attributes from the Dataset.
- IOGP Report 373-07-04 (EPSG Guidance Note 7-4) – EPSG Database and SQL Script user guide, provides guidance for users of the EPSG Database and SQL scripts; these may be obtained from the EPSG Registry's Download Dataset page.
- IOGP Report 373-07-05 (EPSG Guidance Note 7-5) – EPSG null and copy transformations to WGS 84, explains aspects of the policies for the inclusion in the EPSG Dataset of datum ensembles and so-called null coordinate transformations to WGS 84, including limitations in the description of WGS 84 through code EPSG:4326.
- IOGP Report 373-07-06 (EPSG Guidance Note 7-6) – EPSG Dataset - Policies and procedures for data management, documents strategy for populating the EPSG Dataset.

The complete texts may be found on the EPSG Registry web site under Support Documentation.

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