Am I using vanilla NAD 1983

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03-18-2016 07:47 AM
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AngelaGruber
New Contributor II

Hello everyone,

I have a question about NAD 83.  I am not very knowledgeable about the
different versions of NAD 83, but I am hoping someone can help.  My organization uses GIS data in State Plane,
specifically this:  NAD_1983_StatePlane_Texas_South_Central_FIPS_4204_Feet.  When I look at the Coordinate System list under Data Frame Properties in ArcMap, I see a lot of choices, such as:  NAD 1983 (2011) (US Feet), NAD 1983 (CORS96) (US Feet), NAD 1983 HARN (US Feet), and NAD 1983 (US Feet).  We use the last one.

Is it correct to assume that NAD 1983 (US Feet) is the original version of NAD 1983 (1986)?

I read another discussion that touched on this topic, but it
was really more complicated, involving transformations with 7 parameters,
etc.  It was a bit over my head.  I just want to know if I am working in vanilla NAD or something else.

I have attached a screen shot of the Coordinate System list.

Thanks for your help,

Bea

1 Solution

Accepted Solutions
MargaretMaher
Esri Contributor

Hello Bea,

In reply to your original post, the coordinate system NAD_1983_StatePlane_Texas_SouthCentral_FIPS_4204_Feet is indeed referring to the original definition of the NAD 1983 datum, that was published by the National Geodetic Survey in 1986.  This new datum was created on the GRS 1980 spheroid, and is quite a bit more accurate than the old NAD 1927 datum that had been created for North America in the 1930's.  The National Geodetic Survey (NGS) then added NAD 1983 HARN for the various states over the years.  Our Knowledge Base article 40878 lists the years in which these various HARN transformation grids were published, because those were done pretty much on a state by state basis.  Next  the NGS added NAD 1983 (CORS96 - HARN for the entire US and all states); NAD 1983 (NSRS 2007); NAD 1983 (PA11 - Pacific Ocean); NAD 1983 (MA11 - Pacific Ocean); and NAD 1983 (2011) with more variations to come. These later variations of the NAD 1983 datum have been created in response to first of all the release of millimeter-accuracy GPS units to the public under former President Bill Clinton, and also increased accuracy and precision of available GPS devices.   New GPS devices, if used correctly, are sensitive enough to capture differences in position due to continental drift over time.  For a lot of the world this is really not a big concern - the difference between NAD 1983 and NAD 1983 2011 for most of the United States is a few inches.  The places where this difference is significant is in tectonically active areas, where continental drift is substantial, like along the Pacific Coast, Alaska and Hawaii.  If you are concerned, or interested in the offset for your area, go to http://support.esri.com, and look up the above article 40878.  At the bottom of the article, there is a link to the new datum transformation utility that was created by the NGS called GeoCON.  This utility will transform between NAD 1983 HARN and these other newer versions of NAD 1983 - NSRS2007, 2011, etc.  PA11 and MA11 are used for the Pacific Ocean so these would not be of concern for your data in Texas.  You can enter coordinates in degrees-minutes-seconds or decimal degrees to get those coordinates transformed to one of the new datums.  NAD 1983 2011 is the most recent version.  Knowing the amount of datum shift for your area, you can then decide if you should transform your data to the new datum definitions.  Hope this is helpful!

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12 Replies
AdrianWelsh
MVP Honored Contributor

Hi Angela,

That is a great question. And that was my impression as well. I always 'understood' the NAD 1983 US Feet system to be the original version and all the other versions were 'corrections' and other types of 'potentially more accurate' systems. I will be curious to hear what others say though.

Cheers,

Adrian

AngelaGruber
New Contributor II

Thank you, Adrian.  That is what I've been thinking.  This, of course, leads me to the next question of whether my GPS data, processed against a base station using WGS84 (ITRF00) should be transformed into vanilla NAD 83 or left alone.

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ChrisSmith7
Frequent Contributor

As I understand, NAD 83 was the original (as an upgrade to NAD 27). NAD 83 HARN was the first attempt at making NAD 3D... NAD 83 and NAD 83 (CORS96) are sometimes equivalent, e.g. you post-processed GPS points with CORS control points. NAD 83 (2011) is the latest refinement - here's a good slideshow to review:

http://www.wsrn3.org/CONTENT/Reference/Presentation_2011_Adjustment_Signani.pdf

AngelaGruber
New Contributor II

Thank you for the reply, Chris.  My next question flows from this.  My GIS data is assumed to be in vanilla NAD 83 (from the above discussion).  I have some GPS data that will be post-processed and added to the GIS data.  If I post-process the GPS data against a base station that uses WGS 84 (ITRF00), should I apply a transformation?  My hunch is to use the WGS 84 to NAD 83 transformation_1 as that is a zero shift transformation.  I thought to use this because WGS 84 is equivalent to vanilla NAD 83, and therefore no shift is needed.  However, others have mentioned using the WGS 84 to NAD 83 transformation _5 because this is the latest transformation.  This makes sense from the stand point that it is the latest, however, I am not using the latest NAD 83 (I don't think).  Wouldn't using transformation_5 adjust my GPS data to a later version of NAD 83, such as NAD 83 (CORS 96)?  If I did that, would my GPS data be misaligned with the (vanilla NAD 83) GIS data?

I hope that made sense...:)

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ChrisDonohue__GISP
MVP Alum

Sorry to muddy things up, but there appears to be another "flavor" of NAD83 out there:

Latest version of North American Datum

The United States National Spatial Reference System NAD 83(2011/MA11/PA11) epoch 2010.00, is a refinement of the NAD83 datum using data from a network of very accurate GPS receivers at Continuously Operating Reference Stations (CORS). 

Source:  North American Datum - Wikipedia, the free encyclopedia

Melita Kennedy

Chris Donohue, GISP

AdrianWelsh
MVP Honored Contributor

Chris, that is quite muddy. Referring to Melita is a good idea. I would also mention Margaret Maher

0 Kudos
MargaretMaher
Esri Contributor

Hello Bea,

In reply to your original post, the coordinate system NAD_1983_StatePlane_Texas_SouthCentral_FIPS_4204_Feet is indeed referring to the original definition of the NAD 1983 datum, that was published by the National Geodetic Survey in 1986.  This new datum was created on the GRS 1980 spheroid, and is quite a bit more accurate than the old NAD 1927 datum that had been created for North America in the 1930's.  The National Geodetic Survey (NGS) then added NAD 1983 HARN for the various states over the years.  Our Knowledge Base article 40878 lists the years in which these various HARN transformation grids were published, because those were done pretty much on a state by state basis.  Next  the NGS added NAD 1983 (CORS96 - HARN for the entire US and all states); NAD 1983 (NSRS 2007); NAD 1983 (PA11 - Pacific Ocean); NAD 1983 (MA11 - Pacific Ocean); and NAD 1983 (2011) with more variations to come. These later variations of the NAD 1983 datum have been created in response to first of all the release of millimeter-accuracy GPS units to the public under former President Bill Clinton, and also increased accuracy and precision of available GPS devices.   New GPS devices, if used correctly, are sensitive enough to capture differences in position due to continental drift over time.  For a lot of the world this is really not a big concern - the difference between NAD 1983 and NAD 1983 2011 for most of the United States is a few inches.  The places where this difference is significant is in tectonically active areas, where continental drift is substantial, like along the Pacific Coast, Alaska and Hawaii.  If you are concerned, or interested in the offset for your area, go to http://support.esri.com, and look up the above article 40878.  At the bottom of the article, there is a link to the new datum transformation utility that was created by the NGS called GeoCON.  This utility will transform between NAD 1983 HARN and these other newer versions of NAD 1983 - NSRS2007, 2011, etc.  PA11 and MA11 are used for the Pacific Ocean so these would not be of concern for your data in Texas.  You can enter coordinates in degrees-minutes-seconds or decimal degrees to get those coordinates transformed to one of the new datums.  NAD 1983 2011 is the most recent version.  Knowing the amount of datum shift for your area, you can then decide if you should transform your data to the new datum definitions.  Hope this is helpful!

AngelaGruber
New Contributor II

Thank you, Margaret.  I needed to verify my suspicions on this.  Because my organization's data is in vanilla NAD 83, I think I need to change the transformation I am using from WGS 84 to NAD 83 transformation_5 back to WGS 84 to NAD 83 transformation_1.

I do appreciate all your help.

0 Kudos
MargaretMaher
Esri Contributor

Angela,

Please do not use the transformation NAD_1983_TO_WGS_1984_1.  This is an old transformation that treats these two datums as being identical, and they are not.  The semi-major axes, between the center of the earth and the Equator are the same, but the semi-minor axes, from the center of the earth to the poles are different lengths, so the two spheroids and datums have different curvatures.  You will notice that this transformation has parameter values of 0, which means that this transformation does not do anything except rename the datum.  In ArcGIS Desktop, the most accurate transformation that is available between NAD 1983 and WGS 1984 is WGS_1984_(ITRF00)_To_NAD_1983.  Note that geographic transformations work with equal accuracy in either the forward or the reverse direction, as noted in Knowledge Base article 21327.  Please post if you have additional questions and thank you!  Margaret