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GPS on Bench Marks Webinar

Learn about GPS on bench marks, GEOID12B creation, residuals calculation, rejection codes, and dataset analysis in this informative webinar. Discover the significance of different heights and get insights from surveyors and geocachers.

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GPS on Bench Marks Webinar

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  1. GPS on Bench Marks Webinar March 15, 2017

  2. Why? There are ~430,000 published First and Second Order Bench Marks United States and Territories ~27,000 GPS on bench marks used to create GEOID12B ~40,000 at a distance more than 30 km from a BM used in 12B ~300,000 bench marks with SCALED positions ~200,000 bench marks not recovered in 30 years

  3. Who and How? • Surveyors • OPUS-Share • OPUS-Projects • Surveyors and Geocachers • Mark Recovery • RTK • Handheld • Cell phone

  4. Different Heights H - Orthometric Height (elevation) h - Ellipsoid Height N – Geoid Height/Undulation

  5. What is a residual and how is it calculated? H ≈ h - N residual = H + N - h Causes can be from: Old/bad leveled height, bad ellipsoid height Time between heights, stability/movement Limited data in area

  6. GEOID12B GPS on BM dataset Rejection Codes (flag) Code S – The State Advisor (now called Regional Geodetic Advisors) recommended it be dropped (subsidence, stability, etc.) Code h – The residual ellipsoid height errors from the NAD 83 (2011) project indicated that the point was too noisy Code H – The orthometric height was suspect Code N – The residual errors during geoid modeling were too high S h H N

  7. Dave Zilkoski GPS World article Analyzing NGS’ GPS on benchmark dataset Used to make GEOID12B Discusses evaluating residuals http://gpsworld.com/analyzing-ngs-gps-on-bench-mark-dataset-used-to-make-geoid12b/

  8. Zilkoski, GPS World http://gpsworld.com/analyzing-ngs-gps-on-bench-mark-dataset-used-to-make-geoid12b/

  9. 28.5 cm difference 30km apart Zilkoski, GPS World http://gpsworld.com/analyzing-ngs-gps-on-bench-mark-dataset-used-to-make-geoid12b/

  10. Questions? GPS on Bench Marks team ngs.gpsonbm@noaa.gov March 15, 2017

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