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Notice To Adopt a Standard Model for Mathematical Vertical Datum Transformations

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National Geodetic Survey (NGS), National Ocean Service (NOS), National Oceanic and Atmospheric Administration.




The purpose of this notice is to announce a decision by the Federal Geodetic Control Subcommittee (FGCS) to recommend adoption of a standard method for mathematical transformations between the vertical geodetic datums: The National Geodetic Vertical Datum of 1929 (NGVD 29) and the North American Vertical Datum of 1988 (NAVD 88). These methods are designated, in descending order of accuracy: (1) The recomputation or readjustment of survey observations method, (2) the mathematical transformation method, and (3) the average shift method. In order to maintain consistency of results and to minimize misuse associated with the mathematical transformation method, FGCS recommends software identified as VERTCON (Vertical Conversion) as a Federal standard.


Individuals or organizations wishing to submit comments on the adoption of VERTCON as the standard method, should do by August 10, 2007.


Written comments should be sent to the attention of David Doyle, Chief Geodetic Surveyor, Office of the National Geodetic Survey, National Ocean Service (N/NGS2), 1315 East-West Highway, Silver Spring, Maryland 20910, fax 301-713-4324, or via e-mail

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Requests for additional information should be directed to David Doyle, Chief Geodetic Surveyor, National Geodetic Survey (N/NGS2), 1315 East-West Highway, Silver Spring, MD 20910; Phone: (301) 713-3178.

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The intent of this notice is to standardize a vertical datum transformation method when a mathematical transformation is desired. FGCS selected the method incorporated in the software identified as VERTCON. It is not the intent of the notice to declare when to use a datum transformation or by what method but only to declare that when a mathematical transformation is appropriate, VERTCON is recommended. Note that VERTCON is not appropriate to transform between NGVD 29 and NAVD 88 for first-, second-, or third-order heights, as defined in the Federal Geodetic Control Committee (FGCC), Standards and Specifications for Geodetic Control Networks, and retain first- or second-, or third-order accuracies in the results. Method 1, recomputation or readjustment of survey observations, is usually more appropriate to maintain first-, second-, and third-order FGCC accuracies.

VERTCON can be accessed for on-line computation from the NGS Geodetic Tool Kit at​TOOL/​Vertcon/​vertcon.html, or copies of the VERTCON software are available for free download from the NGS Web site​PC_​PROD/​pc_​prod.shtml#VERTCON.

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Dated: July 5, 2007.

Elizabeth R. Scheffler,

Associate Assistant Administrator for Management, Ocean Services and Coastal Zone Management.

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[FR Doc. 07-3377 Filed 7-10-07; 8:45 am]