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Clarke 1866   Jessie Quinn Mar 08, 2005
Re: Clarke 1866   Melita Kennedy Mar 08, 2005
Re: Clarke 1866   Kim Fisher Dec 06, 2007
Re: Clarke 1866   Melita Kennedy Dec 07, 2007
Re: Clarke 1866   Kim Fisher Dec 10, 2007
Re: Clarke 1866   Melita Kennedy Dec 10, 2007
Re: Clarke 1866   Joel Cusick Dec 16, 2007
Re: Clarke 1866   Chris Barnes Nov 04, 2008
Re: Clarke 1866   Melita Kennedy Nov 04, 2008
Re: Clarke 1866   Nathaniel Roth Dec 03, 2008
Re: Clarke 1866   scott pontifex Apr 20, 2009
Re: Clarke 1866   Melita Kennedy Apr 21, 2009
Re: Clarke 1866   scott pontifex Apr 21, 2009
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Subject Clarke 1866 
Author Jessie Quinn 
Date Mar 08, 2005 
Message I have XY point data that is in decimal degrees (WGS84 Datum). I have been attempting to project the coordinate system by importing the spatial reference properties from another layer. The coordinate system is Clarke_1866_Albers. However, when I get to the point that says "Geographic transformation," I am not sure what transformation to use. The datum is D_Clarke_1866. Everything I have tried selecting gives me: "Undefined geographic transformation." I am (quite obviously) a newbie here...what am I doing wrong? 
   
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Subject Re: Clarke 1866 
Author Melita Kennedy 
Date Mar 08, 2005 
Message Clarke 1866 is a spheroid, not a true datum. We do have a geographic coordinate system called 'GCS_Clarke_1866' but only for data where the true datum/geographic coordinate system isn't known. There are no transformations between Clarke 1866 and WGS84.

A lot of 'Clarke 1866' data is really NAD27. But sometimes it's not. 'Clarke 1866' is the default spheroid for ArcInfo workstation data, so if someone didn't specify a datum when setting the coordinate system, the software used Clarke 1866.

So you try changing the output coordinate system to NAD27 Albers. At that point you will be able to set a geographic transformation. For information on what's available look in the desktop help, table of contents, map projections, first topic (if using 9.0) and look for the link to the geographic transformations PDF file.

Melita Kennedy
ESRI Product Specialist 
  Melita Kennedy
ESRI Product Specialist 
   
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Subject Re: Clarke 1866 
Author Kim Fisher 
Date Dec 06, 2007 
Message Hello,

I have a bunch of rasters and shapefiles in GCS_WGS_1984. I've been asked to deliver data with the following:

Clarke_1866_Albers
Albers
False_Easting: 0.000000
False_Northing: 0.000000
Central_Meridian: -119.008333
Standard_Parallel_1: 29.500000
Standard_Parallel_2: 45.500000
Latitude_Of_Origin: 23.000000

I've seen a number of posts in the forums about converting in the other direction. And I've seen posts like this that mention that it's not always clear what people mean by "Clarke 1866." So as a relative newcomer, I'd like to ask for your collective wisdom. Given these specifications, what would you do? Can you tell exactly what datum I should convert to, and what geographic transformation to use? Thanks for any guidance. 
   
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Subject Re: Clarke 1866 
Author Melita Kennedy 
Date Dec 07, 2007 
Message Hi Kim,

Because the data is US data, Clarke 1866 = NAD27. It's still possible that their data could be NAD83 or a mix of NAD27 and NAD83, mislabelled. This is because Clarke 1866 was used as a default spheroid/ellipsoid in ArcInfo workstation.

You might try to push them a little--can you get some data that you can use to check your converted data against?

If we assume that the data is really NAD27, and convert your data so, but their data is really NAD83, and just mislabelled, the data could be off a hundred meters.

Let's assume their data is NAD27.

There are transformations that convert directly between NAD27 and WGS84, but they're not the most accurate. What you should do is WGS84-to-NAD83-to-NAD27. The project will only show you the NAD27/WGS84 transformations.

However, we can use a new 9.2 tool to make a direct transformation between NAD27 and WGS84 using the NADCON conus file. The tool is, "Create custom geographic transformation" and it's in the projections and transformations section of the data management toolbox.

Start the tool. Give the transformation a name, and choose Clarke 1866 (it's in the spheroid-based folder) for the input coordinate system, and WGS 1984 for the output coordinate system. This is opposite what you want to do, but the transformation will work in both directions. For the method choose NADCON. For the Grid Dataset Name, use "conus" (no quotes).

Once the transformation is defined, use the Project tools to convert your data.

Melita 
  Melita Kennedy
ESRI Product Specialist 
   
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Subject Re: Clarke 1866 
Author Kim Fisher 
Date Dec 10, 2007 
Message Melita -- just a quick note to thank you for the helpful, specific response. I followed your advice and it worked flawlessly. I assume that the difference between the transformation you helped me make and the stock ones is only the NADCON/conus specification?

Thanks again,
Kim 
   
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Subject Re: Clarke 1866 
Author Melita Kennedy 
Date Dec 10, 2007 
Message Hi Kim,

The new transformation works the same as NAD_1927_To_NAD_1983_NADCON, just between "Clarke 1866" and NAD83 instead. The NADCON/CONUS is the best transformation available for the lower 48 states, better than the direct NAD27/WGS84 transformations.

Melita 
  Melita Kennedy
ESRI Product Specialist 
   
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Subject Re: Clarke 1866 
Author Joel Cusick 
Date Dec 16, 2007 
Message Hi Melita,

The tool is a fantastic work-a-round, but it perpetuates the issue that WGS84 is the same as NAD83, since Kim is assuming the WGS84 data is really NAD83 to apply NADCON. Depending on the input coordinates, if the user had a table of "true" WGS84 coordinates derived from modern GPS, then this method of skirting WGS84-NAD83-NAD27 using NADCON has imparted a 1+meter horizontal shift to the data, then if the user took WGS84, transformed to NAD83 using _5, and then NADCON to NAD27.

Datum Tarpit Joel 
   
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Subject Re: Clarke 1866 
Author Chris Barnes 
Date Nov 04, 2008 
Message I am able to 'see' the new transformation I have created in the Environment Settings, Geographic Transformations Names widow. And can add it successfully to the list of transformation methods.

However when I attempt to project my data using this newly created transformation I am unable to select it from the transformation list.

Thank you for your help! 
   
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Subject Re: Clarke 1866 
Author Melita Kennedy 
Date Nov 04, 2008 
Message Hi,

Usually, that means that there's still something not quite the same in one of the geographic coordinate systems in the new transformation versus what the data's using. The entire definition must be the same, including the names.

Melita 
  Melita Kennedy
ESRI Product Specialist 
   
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Subject Re: Clarke 1866 
Author Nathaniel Roth 
Date Dec 03, 2008 
Message I just noticed this post.

If you've got a dataset that originated with the old Teale Geographic Data Center in California, the Albers_1866 projection is (almost always) an incorrectly named California Teale Albers NAD27.

At some point a projection file was created incorrectly and it got used for most of the data collection. Newer data is from gis.ca.gov is correctly projected, but there are still some older datasets that are incorrect. 
   
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Subject Re: Clarke 1866 
Author scott pontifex 
Date Apr 20, 2009 
Message dear list.
I have some old map files from US Census Bureau Tiger Line File for the Federated States of Micronesia (located in the Northern Pacific). These appear to have been in NAD27 datum and clarke1866 spheroid. Using the geographic transformation NADCON conus would not make sense but I somehow need to convert to WGS and I was wondering how to create or find a transformation from NAD27 to NAD83 or WGS84 that would help me.

Scott 
   
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Subject Re: Clarke 1866 
Author Melita Kennedy 
Date Apr 21, 2009 
Message Hi Scott,

Any particular islands? NGS has published a few transformations. Open the geographic_transformations.pdf file that's in your install's Documentation folder and search for the island names.

If you can't find anything, also try http://www.epsg-registry.org (or http://www.epsg.org).

Melita 
  Melita Kennedy
ESRI Product Specialist 
   
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Subject Re: Clarke 1866 
Author scott pontifex 
Date Apr 21, 2009 
Message Hi Melita

I am most interested in Kosrae, Pohnpei, Chuuk and Yap Islands these make up the Federated States of Micronesia. I found references to GCS_Pohnpei
and a transformation in ArcGIS.

Using EPSG Geodetic Parameter Dataset I found a few references to Federated States of Micronesia - Caroline Islands and Yap Islands and one other tranformation known as Kusaie 1951 to WGS 84 (1)

I'm still trying to work it out. Thanks for your help
Scott