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Technical Article   HowTo:  Select the correct geographic (datum) transformation when projecting between datums

Article ID: 21327
Software:  ArcGIS - ArcEditor 8.1, 8.1.2, 8.2, 8.3, 9.0, 9.1, 9.2, 9.3, 9.3.1, 10 ArcGIS - ArcInfo 8.0.1, 8.0.2, 8.1, 8.1.2, 8.2, 8.3, 9.0, 9.1, 9.2, 9.3, 9.3.1, 10 ArcGIS - ArcView 8.1, 8.1.2, 8.2, 8.3, 9.0, 9.1, 9.2, 9.3, 9.3.1, 10 ArcGIS for Desktop Advanced 10.1 ArcGIS for Desktop Standard 10.1 ArcGIS for Desktop Basic 10.1
Platforms: N/A

Summary

It is necessary to specify a geographic (datum) transformation when using the ArcToolBox Project Wizard (ArcGIS version 8.x) or Project Tool (ArcGIS version 9.x) to project shapefiles or geodatabase feature classes between different geographic coordinate systems (datums).

A user must also select an appropriate Geographic (datum) transformation in ArcMap, when displaying data that are projected on different datums.

Procedure

Click a link in Related Information to access a list of the geographic (datum) transformation methods available in ArcGIS and the geographic areas for which these transformations are appropriate, for your version of ArcGIS Desktop.


 Datum transformations work in either direction. For example, the transformation listed as NAD_1927_to_NAD_1983_NADCON transforms from NAD 1983 to NAD 1927, as well as from NAD 1927 to NAD 1983.



Related Information


Created: 1/2/2002
Last Modified: 9/6/2013

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Comments

By maskari - 10/10/2012 1:05 PM

Other - See details below.

The same information is available via a Microsoft Access database as part of the EPSG (European Petroleum Survey Group) Geodetic Parameter Dataset and can be downloaded from this link - http://www.epsg.org/databases/Discv8_0.html

By gnewburyiv - 09/12/2012 12:44 PM

Other - See details below.

Is there an excel or other tabular format for this information? It is nice to have a lookup PDF but it would be nice to have it in a table that one could easily reformat for programming. Also it would be nice to have a shapefile/feature class with the bounding boxes of where each transformation is appropriate.

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By Anonymous - 02/28/2011 2:36 PM

I have suggested related resources/links that can enhance this article. See below.

NAD83 to WGS84_5 lat long signifies its not suitable for use in Alaska (North). I would disagree, until CORS96 showed up, the _5 has been used up to now, and in many cases (Garmin, low end Trimble), those params are entirely suitable for us. I would suggest that this article implies its not for Alaska, and it is.

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By Anonymous - 11/13/2008 8:29 AM

I would like to see a new article that discusses the topic outlined below.

It is necessary to specify a geographic (datum) transformation when using the ArcToolBox Project Wizard (ArcGIS version 8.x) or Project Tool (ArcGIS version 9.x) to project shapefiles or geodatabase feature classes between different geographic coordinate systems (datums). IT IS NOT CORRECT TO "PROJECT" BETWEEN DIFFERENT GEOGRAPHIC COORDINATE SYSTEMS. THIS CONVERSION IS ACHIEVED BY THE TRANSFORMATION. PROJECTION IS ONLY DONE AFTERWARDS FROM THE LOCAL/FINAL ELIPSOID TO THE FLAT EARTH EASTING NORTHING GRID. ALL THE COORDINATE SYSTEM ARTICLES SEEM SIMILARLY CONFUSING.

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By Anonymous - 11/03/2008 2:54 PM

Other - See details below.

Why is this information inside a word document inside a zip file on your web site - could you make it any harder to find? Put it in the help files distributed with your software so that your users can find it!!!

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By Anonymous - 10/14/2008 6:50 AM

The article has missing, misleading, or conflicting information.

The article says that it is "necessary" to specify a datum transformation. Yet the Project tool wizard very clearly uses the word "optional" when asking for the transformation input from the user. I see a direct conflict between the words "necessary" and "optional". Surely some explanation is in order. Further, the article needs to tell us far more about how to correctly choose a transformation. There are many choices; how do users make the best, informed choice?

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By Anonymous - 02/14/2007 12:47 PM

Other - See details below.

Why isn't this table of transformations in the included desktop and developer help. You can't use the project tool when going between datums without specifying a transformation and there is nothing in the help that tells you what the different options mean. Unfriendly....

By Anonymous - 01/16/2007 1:04 PM

The article contains a typographical or grammatical error.

Hi, I reported this before about your PEgt_namewhere.doc file. Please remove spaces from all three of: "New_Zealand _1949..." entries When one "cut and paste" syntax for use i will fail because there should not be any spacing. Thank you.

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By Anonymous - 09/13/2006 4:49 PM

The article contains a typographical or grammatical error.

Hi, I am sure I reported this before but is still uncorrected. Your third link under "Related Information" will download a doc file. Please note there is a space after .....Zealand New_Zealand _1949_To_NZGD_2000_1_3PAR 1566 New Zealand New_Zealand _1949_To_NZGD_2000_2_7PAR 1701 New Zealand New_Zealand _1949_To_NZGD_2000_3_NTv2 1568 New Zealand There should be no spaces. Regards Edward

By Anonymous - 03/22/2006 2:40 PM

Why isn't this in the help for ArcMap? It would be great if when I was presented with 5 options for Geographic Transformation, the help system would tell me the data that is in this pdf.

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By Anonymous - 10/05/2005 8:36 PM

Hi, I found errors in PE9xtrans.zip from link "ArcGIS Projection Engine v.9.x...." The actual problems: New_Zealand _1949_To_NZGD_2000_1_3PAR 1566 New Zealand New_Zealand _1949_To_NZGD_2000_2_7PAR 1701 New Zealand New_Zealand _1949_To_NZGD_2000_3_NTv2 1568 New Zealand There is a space after "New_Zealand" and the next "_". Regards Edward

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By Anonymous - 11/15/2004 6:42 AM

I needed to know how to choose an appropriate coordinate system for polar regions - not for the USA.

By Anonymous - 12/30/2003 2:49 PM

You could improve by making more users aware of this information. I happened across it with technical support. Excellent work, otherwise! Pete

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By Anonymous - 01/30/2003 8:46 AM

salut tous

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