GPS On Bench Marks (GPSBM) Used To Make GEOID09

Updated 2009 Sep 14

Each of the below regions uses variants of the NAD 83 reference frame and a local vertical datum. Several versions of NAD 83 exist conforming to significant plates: Pacific, Marianas, and North America. Likewise, each region has its own vertical datum. It is not possible to level across water, so islands will have selected a tide gage to serve as the local datum point and all leveling is tied to that site. The only exception to this is Hawaii. No tide gage was selected in the Hawaiian Islands. Hence, GEOID09 in Hawaii transforms between NAD 83 (PAC00) and the same geopotential (geoid) surface as the USGG2009 model (a gravimetric geoid surface).

Items that are listed in the below table include the final GPSBM files for each region as both Excel spreadsheets and text files as well as thumbnail images linked to larger images showing the distribution of the GPSBM's. The island regions are smaller and more consistent, so no significant points were dropped. For CONUS, 1002 points were dropped based on the criteria given in the rejection code: 'S' for State adviser requested (216 total), 'h' for excessive ellipsoidal height error for those where it was available (970 total), and 'H' where the residual orthometric height was too large with respect to neighboring points (16 total). Even though over a thousand were rejected, over 19,443 were kept. One other point was rejected because it fell physically too close to another point for computation. You can look at a image of the rejected CONUS points below.

GPS on BM - CONUS	GPS on BM - CONUS Rejected	GPS on BM - Alaska
GPS on BM - American Samoa	GPS on BM - Guam	GPS on BM - CNMI

• Format of GPS/Bench Mark Text Files

NAVD88 - NORTH AMERICAN VERTICAL DATUM OF 1988
ASVD02 - AMERICAN SAMOA VERTICAL DATUM OF 2002
GUVD04 - GUAM VERTICAL DATUM OF 2004
NMVD03 - NORTHERN MARIANAS VERTICAL DATUM OF 2003

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