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Coordinate conversion - NAD 27 to WGS 84   Gavin Glore Nov 30, 2005
Re: Coordinate conversion - NAD 27 to WGS 8...   Melita Kennedy Nov 30, 2005
Re: Coordinate conversion - NAD 27 to WGS 8...   Gavin Glore Dec 01, 2005
Re: Coordinate conversion - NAD 27 to WGS 8...   Melita Kennedy Dec 02, 2005
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Subject Coordinate conversion - NAD 27 to WGS 84 
Author Gavin Glore 
Date Nov 30, 2005 
Message I am trying to convert a set of about 2000 coordinates from decimal degree NAD 27 to dd WGS 84, any suggestions? I don't need to be able to display the data in WGS84, I just need the actual coordinates converted from 27 to 84 so I can copy them into an Access datatable. I am hoping that there is a free conversion utility that will work for this. 
   
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Subject Re: Coordinate conversion - NAD 27 to WGS 84 
Author Melita Kennedy 
Date Nov 30, 2005 
Message Well, there's converting, and there's converting.

The best way is to use a tool that supports the NADCON method or software and convert the coordinates to NAD83. At that point, you might also use NADCON (but called the HARN method in ESRI software) to convert from NAD83 to NAD83 HARN, aka HPGN. There are some transformations that convert from NAD83/NAD83HARN to WGS84, but at least for the lower 48, the differences are under a meter, so the data accuracy may not warrant it.

NGS (http://www.ngs.noaa.gov) publishes both NADCON and CORPSCON programs. Both have file-based capabilities, but the file formats are bit convoluted. NADCON and HARN need supporting binary files to calculate the shifts.

There are simpler transformations that go directly from NAD27 to WGS84, but they aren't as accurate. They are also area of use based. In ESRI software, there are 25.

If you have 3.x, you could convert the coordinates to a shapefile, use the Projection Utility (it supports NADCON/HARN), and then add the new XY values to the new shapefile and export them.

Melita Kennedy
ESRI Product Specialist

 
  Melita Kennedy
ESRI Product Specialist 
   
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Subject Re: Coordinate conversion - NAD 27 to WGS 84 
Author Gavin Glore 
Date Dec 01, 2005 
Message I have a ShapeNadcon Converter program that will get me to Nad 83, but I have never delved into the world of 83 HARN. Can I convert from 83 to 83 Harn within ArcView, or do I need a seperate utility? I don't think I will need to get to WGS 84 if the accuracy as close as you indicated. Thanks for the help. 
   
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Subject Re: Coordinate conversion - NAD 27 to WGS 84 
Author Melita Kennedy 
Date Dec 02, 2005 
Message If it's already a shapefile, the ArcView Projection Utility should support the HARN files. They're generally state-based. There are a few states whose files haven't been published.

The differences between NAD83 and NAD83 HARN are sub-meter too, so...

Melita 
  Melita Kennedy
ESRI Product Specialist