GPS On Bench Marks for GEOID03

Created December 24, 2003 DRR

Updated February 17, 2009 DRR

(changes since last update are shown in RED)

For more background on how GPS on Bench Marks (GPSBM's) are used in combinaton with a gravimetric geoid to create a hybrid geoid, see the discussion for GPSBM99.

The GPSBM2003 data set contains significant differences as compared to GPSBM99. There were 13,809 points in the original database pull, but only 13,554 were useful. Some were rejected as outliers (123), while another 132 were dropped because they fell in the southern Louisiana subsidence region. Since this subsidence has been modeled for some areas, it was possible to determine corrected values for 52 of the 132 points. The resulting subset of 13,606 points consists of points retained throughout most of the U.S. (13,554) and those for southern Louisiana (52).

An additional 579 points were made available from Natural Resources Canada. These additional points help to control the behavior of the Least Squares Collocation method along the northern border. The total number of points for GPSBM2003 is then 14,185. These data are shown in the below image.

The data presented below refer to NAD 83 and NAVD 88. They are listed first as the 579 Canadian points, then the 123 rejected points (look for the flag (*) in the 80th column), then the 13554 CONUS points, and lastly the 52 points in southern Louisiana. The Canadian data all have PID's starting with CANxxx, while the southern Louisiana data all have PID's starting SLA0xx.

For the Southern Louisiana data, follow the below link to find the cross-reference between the SLA0xx PID and its corrected orthometric height and the original PID and height as are currently given in the NGS database. The expectation is that these heights will be updated and the database will reflect the revised heights at a future date.

This was updated in 2005 to include points in southern Louisiana adjusted for Vertical Time-Dependent Positioning (VTDP). Primarily the above SLA0xx points were replaced by a net of 87 points (several others in the region were rejected). These updated points were used to make the standing GEODI03 model available for download. The original SLA0xx data were used to make the original, and now deprecated, grid #7. Note that these points were loaded into the database, so no false PID's were generated.

As a final note, the decision was made at that time to retain the GEOID03 name, even though the VTDP changes occurred in 2005. Hence, the original and final model both retain the GEOID03 name and 'deprecated' is applied to the original version.

• GPS/Bench Marks in NAD 83 Reference Frame (Original with deprecated Louisiana data)
• GPS/Bench Marks in NAD 83 Reference Frame (Revised in 2005 to include VTDP-modified Louisiana data)
• Format of GPS/Bench Mark File
• Documentation of the GPS/Bench Mark Files
• Postscript Image of GPS/Bench Mark Map (992,809 bytes)
• Cross-reference table for PID's & orthometric heights in southern Louisiana
• GEOID03

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