DEFLEC99

First created 10/01/1999   DAS.

Last updated 11/16/2009   

DEFLEC99 is a companion product derived from GEOID99 representing the deflections of the vertical at the surface of the Earth. The deflection of the vertical is the departure of a plumb bob's true pointing from the ellipsoidal normal direction. These quantities are typically a few arc seconds, but can reach an arc minute of departure.

Deflections are used to relate the orientation of a locally-leveled instrument, such as a theodolite, to a spatial reference system. Important uses are corrections to zenith distance (vertical angle) measurements, and the conversion between astronomic and ellipsoidal azimuths (the Laplace correction).

DEFLEC99 is comprised of both north-south (Meridian component, designated as "Xi") and east-west components (Prime Vertical component, designated as "Eta"). In the United States, Xi ranges from +41 arcseconds (Bahamas), to -38 arcseconds (Bermuda), while Eta ranges from +45 arcseconds (Rockies) to -43 arcseconds (Bermuda). DEFLEC99 products are also available for Alaska, Hawaii, and Puerto Rico & the U.S. Virgin Islands.

North-South Deflections of the Vertical (xi) East-West Deflections of the Vertical (eta)

Data Interactive DEFLEC99 computations Download DEFLEC99 files Information The Official NGS GEOID Page Readme file for DEFLEC99 Technical details Frequently Asked Questions Geophysics of the Geoid On-Line Papers The Geoid Research Page Acknowledgements Related Pages GEOID99 G99BM G99SSS Images of data files used in DEFLEC99 GPS/bench mark data set in GEOID99 The NGSDEM99 1 arcsecond DEM Geoid Research Software Have a geoid question? Contact the Geoid Team

For more information contact NGS Information Services: by e-mail, or call (301) 713-3242, Monday-Friday, 7:00 AM - 4:30 PM eastern time. For questions about this page or downloading problems, contact the Webmaster.

Web site owner: National Geodetic Survey http://www.ngs.noaa.gov/GEOID/DEFLEC99/index.shtml Last Modified: Monday, 16-Nov-2009 09:55:06 EST