Coordinates, Datums and Transformations

Purpose of this page

There has been a lot of chatter on the internet about datums and datum transformations. It is for that reason that I have started this page. The concept of datums can be rather complex and when a question occurs, one should consult an expert about the appropriateness of the methods being employed. As you read through this page and the links that are attached, one principle is evident: the accuracy of the results will be dependent upon the method used. I have recently tried to keep track of some of the information on the various newsgroups where datums are discussed. You can read an edited version of these newgroup discussions . Think of this as an unofficial FAQ.

Links to other pages:

Australian Geodetic Datum. An Updated Explanation of the Geocentric Datum of Australia (GDA) and its Effects Upon Future Mapping by Dr. Will Featherstone, MAIC. (thanks to Will Featherstone for correction)

Australian Surveying and Land Information Group home page on datums and coordinates in Australia with a link to Redfern's formula

Aviation Formulary by Ed Williams with formulas for computing great circel distances. A nice piece written for pilots and other interested in great circle navigation (thanks to Melita Kennedy for the update). Also available is the Great Circle Calculator for use.

CORPSCON. This is a link to an MS-Windows program for coordinate conversion. The software is based on the NADCON and VERTCON software developed by the National Geodetic Survey.

Datum Transformation & Coordinate Conversion, version 4.1 (DTCC4.1) program to perform the transformations of coordinate systems. The program utilized the Molodensky formulas. To download the software the user is required to register with NIMA. (thanks to Peter Dana)

Distortion Properties of Projections from a Differential Geometry. This homepage is just for the purpose of graphic demonstration of map projection in geometric distortion. Site is written by Jian Yi and contains some nice animations of map projections.

EasyTrans homepage. Software that performs a myriad of transformations. The company, run by Dr. Andreas Mathes, offers other services for those who are interested.

A Guide to Coordinate Systems in Great Britain. Contains a 42-page booklet, available in Adobe .pdf format, which is an introduction to mapping coordinate systems and the use of GPS datasets with Ordnance Survey mapping.

How CORS Positions and Velocities were Determined. by the National Geodetic Survey. The text describes the transformation between NAD83 and the ITRF - International Earth Roatation Service (IERS) Terrestrial Reference Frame.

Geodesy for the Layman (TR80-003) A copy of the monograph by Lt. Col. Richard Burkard that discusses the history of geodesy, the figure of the earth, geodetic surveying techniques, geodetic systems, physical geodesy, satellite geodesy and the world geodetic system. An excellent resource for those who want to learn more about geodesy without the mathematics. This is an updated version of the monograph that Burkard published.

Geodesy Foundation Classes by Sam Blackburn that has a C++ code that will calculate the distance between two points (forward and inverse problem).

Geodetic Datum Overview by Peter Dana. This is a part of the Geographer's Craft Project and discusses the basic principles of the figure of the earth and geodetic datums

Geodetic Reference System 1980 by Helmut Moritz

Geospatial Sciences Center. This page has a series of links to information developed by the National Geospatial-Intelligence Agency (formerly the National Imagery and Mapping Agency) on both horizontal and vertical datums. Horizontal Datums gives a simple description of what a datum is, why it is important and how can I check my datum on a map. Vertical Datum is a NIMA publications describing vertical datums, elevations and heights. WGS 84 Description gives a background of geocentric coordinate systems and the WGS 84 relationship with other geodetic systems. This is an overview document. WGS 84 Standard describes the world geodetic system. A Microsoft word file is available for uploading. Another NIMA document Datums, Ellipsoids, Grids, and Grid Reference Systems (DMA Technical Manual 8358.1) contains useful information on these topics.

Hungarian Geodetic Reference System. Discusses the geodetic reference system in Hungary, conversion between the Hungarian system to others, and information on projection systems.

Integration of Local Surveys Into the Canadian Spatial Reference System, by M.R. Craymer. Presented at the Public Works and Government Services Canada (PWGSC) Survey Contracting and CACS Seminar, Edmonton, Alberta, February 24, 1998. Revised May 25, 1998.

International Great Lakes Datum, 1985 (IGLD 1985). This site contains a paper on the Establishment of the International Great Lakes Datum by the Coordinating Committee on Great Lakes Basic Hydraulic and Hydrologic Data.

ITRF. The International Terrestrial Reference Frame home page. Also see Realization and Unification of NAD83 in Canada and the US via the ITRF, by M. Craymer, R. Ferland and R. Snay. Proceedings of the International Symposium of IAG, Section II, "Towards an Integrated Global Geodetic Observing System (IGGOS)", Munich, October 5-9, 1998. Revised 11 March 1999.

Map Projection overview by Peter Dana as a part of The Geographer's Craft..

Map Projections. This is the projection home page from Indiana State University. It contains an introduction to projectssions, a discussion on Tissot's Indicatrix, and examples of different types of projections.

Map Projection Home Page at Hunter College developed by Karen Mulcahy. This site discusses the basics of map projections, gives texts and links to software, references, etc.

Map Projections by Carlos A. Furuti.  A nice look at map projection systems.

MapRef Home Page. This site has the parameters for map projections and reference systems, including the geodetic parameters for Europe. There are also a number of links to terminology, a basic faq, and other bits of information, with an European bent. This site is maintained by S. Voser. (thanks to M. Kennedy for correction)

Maptran. Datum and coordinate system translator which requires Java 1.02 or better.

Mercator Conformal Projection. This site discusses the history of the Mercator Conformal projection, the mathematics, and some external links on this projection.

Mike Cramer's On-Line Publications.  Mike Craymer, Head, Geodetic Networks and Standards at the Geodetic Survey Division in Canada has a wealth of information on geodesy and geodetic issues.

National Geodetic Survey home page. For those interested in NGS coordinate transformation and other geodetic software a lots of choices are possible including: CORPSCON (used to convert between NAD 27 and NAD 83), GPPCCP (converts NAD 27 State Plane Coordinate to/from NAD 27 latitude/longitude), NADCON (transforms between NAD 27 and NAD 83), SPCS83 (converts NAD 83 State Plane Coordinate to/from NAD 83 latitude/longitude), UTMS (converts latitude/longitude to/from UTM coordinates, and VERTCON (computes orthometric height differences between NAVD 88 and NGVD 89). NGS FAQ.

NR 502: Course information on Geodesy, Cartography and Map Reading at Colorado State University, College of Natural Resources with information on datums and coordinate systems as well as map projections.

PCTrans software:  Windows software package developed by the Hydrographic Service, the Netherlands that can be used for datum transformations, map projections, geodetic computations, area computations, and plot functions.

PROJ.4 coordinate transformation package with over 110 projection systems (thanks to Frank Warmerdam for the update).

John Snyder's Map Projection Bibliography: This a up-to-date bibliography of papers dealing with map projections, current to 1996. An excellent resource for anyone wanting to learn more about projections.

Windsway Co. Software: This site includes programs to compute latitude and longitude of a point on a map, compute easting and northing of a point on a map, solve for the direct and inverse geodetic problem, and transform UTM to latitute and longitude and vice versa. These Freeware programs were written by Victor Fraenckel.

This page is maintained by Bob Burtch and was last updated on 8 April 2005. If there are any problems with the links listed here or if there is a site that might be of interest to the geomatics professionals which is not included here, I would appreciate your input. Thanks to the many individuals who have contacted me in the past about mistakes and changes. To err is human and sometimes I am more human than I would like to be.
Please send any comments or suggestions here.