diff --git a/README.md b/README.md index 32c09b6..0addcb4 100644 --- a/README.md +++ b/README.md @@ -10,14 +10,14 @@ To change a coordinate from one datum to another, a mathematical process that mo Transformation grids provide users of spatial data with a simple and nationally consistent method to transform coordinates between datums and potentially allow for a large number of common points to be used in developing the relationship model. -Australian grids of 2D coordinate shifts are provided in the Canadian National Transformation version 2 (NTv2) format as binary files (.gsb) but software provided by ICSM jurisdictions can readily convert them to ASCII format (.gsa). An in-depth explanation of the format can be found in Appendix C of the "GDAit" User Guide and the GDAit Software Documentation available from [www.dtpli.vic.gov.au/geodesy](www.dtpli.vic.gov.au/geodesy) > Geocentric Datum of Australia 1994 (GDA94) > GDA94 useful tools. +Australian grids of 2D coordinate shifts are provided in the Canadian National Transformation version 2 (NTv2) format as binary files (.gsb) but software provided by ICSM jurisdictions can readily convert them to ASCII format (.gsa). An in-depth explanation of the format can be found in Appendix C of the [GDAit] User Guide and the GDAit Software Documentation. -Detailed information on Australian datums and transformations between them is available in the GDA2020 Technical Manual available at [http://www.icsm.gov.au/gda/tech.html](http://www.icsm.gov.au/gda/tech.html) - in particular Chapter 3 and Appendix B describe the transformation methods including background to and area of application of the transformation files. +Detailed information on Australian datums and transformations between them is available in the [GDA2020 Technical Manual] – in particular Chapter 3 and Appendix B describe the transformation methods including background to and area of application of the transformation files. ## Description of the Transformation Grids ### AGD66 <> GDA94 -Full national coverage two-way transformation file – see Appendix B in the GDA2020 Technical Manual available at [http://www.icsm.gov.au/gda/tech.html](http://www.icsm.gov.au/gda/tech.html) for details. +Full national coverage two-way transformation file – see Appendix B in the [GDA2020 Technical Manual] for details. | File | EPSG Transformation Code |-|- @@ -26,7 +26,7 @@ Full national coverage two-way transformation file – see Appendix B in the GDA ### AGD84 <> GDA94 -Full coverage two-way transformation file in those states that originally adopted AGD84 - West Australia, South Australia, Queensland - see Appendix B in the GDA2020 Technical Manual available at [http://www.icsm.gov.au/gda/tech.html](http://www.icsm.gov.au/gda/tech.html) for details. +Full coverage two-way transformation file in those states that originally adopted AGD84 - West Australia, South Australia, Queensland - see Appendix B in the [GDA2020 Technical Manual] for details. | File | EPSG Transformation Code |-|- @@ -34,7 +34,7 @@ Full coverage two-way transformation file in those states that originally adopte ### GDA94 <> GDA2020 -Full national coverage two-way transformation files – See Sections 3.2 and 3.7 in the GDA2020 Technical Manual available at [http://www.icsm.gov.au/gda/tech.html](http://www.icsm.gov.au/gda/tech.html) for details. +Full national coverage two-way transformation files – See Sections 3.2 and 3.7 in the [GDA2020 Technical Manual] for details. Two types of GDA94 – GDA2020 transformation grids have been developed: • Conformal: predominantly plate tectonic motion (~1.8 m NNE) @@ -43,7 +43,7 @@ Two types of GDA94 – GDA2020 transformation grids have been developed: The difference between GDA94 and GDA2020 coordinates is comprised of a conformal transformation component primarily due to plate tectonic motion and an irregular (non-conformal) distortion component. The conformal component accounts for the primary coordinate movement between GDA94 and GDA2020 and replicates a seven-parameter similarity transformation. Conformal grids are also provided for Christmas Island and Cocos (Keeling) Isalnds. The distortion component is attributable to several second-order effects, such as an improved realisation of the global reference frame over time; irregular ground movement since GDA94 was established; and improvements in computation methods since GDA94. These effects vary in magnitude and direction around the country and can be as large as ~0.5 m. -Advice on choosing which grid to use is included in Table 3.4 in in the GDA2020 Technical Manual available at [http://www.icsm.gov.au/gda/tech.html](http://www.icsm.gov.au/gda/tech.html). +Advice on choosing which grid to use is included in Table 3.4 in in the [GDA2020 Technical Manual]. | File | EPSG Transformation Code |-|- @@ -66,3 +66,6 @@ The transformation grids can be accessed by downloading from this project on Git # License [![License: CC BY 4.0](https://img.shields.io/badge/License-CC%20BY%204.0-lightgrey.svg)](https://creativecommons.org/licenses/by/4.0/) + +[GDA2020 Technical Manual]: http://www.icsm.gov.au/datum/gda2020-and-gda94-technical-manuals +[GDAit]: https://www.propertyandlandtitles.vic.gov.au/surveying/geodetic-survey/geocentric-datum-of-australia