Notice to Users
Regarding Local Datum Transformations And GEOTRANS Software
Local Datum Transformations
IMPORTANT NOTE: APPLICATIONS REQUIRING PRECISE POINT POSITIONS SHOULD NOT USE COORDINATES DERIVED FROM A DATUM TRANSFORMATION. USERS WITH HIGH ACCURACY REQUIREMENTS SHOULD CONTACT NGA FOR ADDITIONAL GUIDANCE.
The National Geospatial-Intelligence Agency (NGA) provides an official set of transformation parameters between local datums and WGS 84 in NIMA TR8350.2, Third Edition, 4 July 1997, entitled "Department of Defense World Geodetic System 1984, Its Definition and Relationships with Local Geodetic Systems." The parameters should only be used to transform local datum geodetic coordinates (j , l ) to WGS 84 geodetic coordinates or vice-versa. Datum transformation parameters are available at the NGA web site http://earth-info.nga.mil/GandG/.
Wherever possible, error estimates with one-sigma (1s ) uncertainties are included for each D x, D y, and D z datum transformation component. These estimates do not include the errors of common control station coordinates that were used to compute the shift components. The estimates were assigned after careful consideration of datum transformation solutions and related geodetic information.
Transforming local datum coordinates to WGS 84 coordinates does not improve the accuracy of the transformed coordinates. In fact, transformed geodetic coordinates will be less accurate because the errors in the datum transformation are added to the errors in the original local datum coordinates.
Datum transformation parameters should only be used for the region for which they are specifically defined in NIMA TR8350.2, Appendices B and C. If there is a need for datum transformations outside their defined regions, contact the NGA Customer Service numbers below.
GEOTRANS is the official software for datum transformation and coordinate conversion applications. The datum transformation error estimates output by GEOTRANS are only for guidance in assessing the limitations of the transformed information for a particular application.
phone (314) 676-9124, DSN 846-9124
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