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Using OPUS for ortho elevation

Discussion in 'GNSS & Geodesy' started by billvhill, Jun 12, 2017.

  1. billvhill

    billvhill 3-Year Member

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    The closest bench mark to my project is about 2 miles, I used an OPUS solution at a benchmark set recently by the DOT, the elevation is stamped on the monument, but my solution is about a foot difference. Is that about as good as can be expected? Should I set both units up at the same time and use OPUS projects? Or should I just use the level.
     
  2. Bill93

    Bill93 7-Year Member

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    If your OPUS solution is a foot different from the stamped elevation, I wouldn't trust either without further checking. Did the DOT extend from something on an old geoid model?
     
  3. Lee D

    Lee D 4-Year Member

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    I agree with Bill, I wouldn't trust either of them at face value. The best thing you can do is run levels between two monuments to determine if they fit with each other, especially if you don't own any static processing software.
     
  4. Skeeter1996

    Skeeter1996 2-Year Member

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    I use to think NGS was God in the vertical world. I checked into 5 Benchmarks on a project. None of them matched each other. I'm thinking OPUS is the only way to go anymore. At least you have data to back up your results. The newer Benchmarks along the Interstate were the worst.
     
  5. Scotland

    Scotland 7-Year Member

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    It really depends on so many factors. I spent way more time than I wanted chasing an elevation using OPUS and a vertical BM. Turn out I had some of my own mistakes and then there was some other NGS issues. Questions that come to mind is the order of the BM and how, when, where was it established. How long did you observe on the benchmark? Even though we get fast results with OPUS, you still need some long observation time and on multiple setups on different days.
     
  6. billvhill

    billvhill 3-Year Member

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    When you use OPUS projects, doesn't that calculate the vector between the two GPS points if the were done at the same time
     
  7. MightyMoe

    MightyMoe 6-Year Member

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    In the old days (15 years ago) a foot wouldn't surprise me, today that seems way off. I would need another bench mark at least to be sure there wasn't an outlier. It basically comes down what you are trying to hold, NAVD88, site control, or you are on your own without needing to be "on" anything, say you are doing some remote well site locations. If so OPUS should work well for that. Just set something the next guy can check into.;)
     
    Dave Karoly likes this.
  8. Lee D

    Lee D 4-Year Member

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    Are you trained on OPUS Projects? They only allow access to people who have been to the class.

    OPUS Projects does calculate the vector but it's no substitute for baseline processing with a program like TBC or LGO. I wouldn't use it for a single baseline.
     
  9. billvhill

    billvhill 3-Year Member

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    Funny thing the elevation is stamped to 3 places, but the data sheet only has an ellipsoid height, the orthometric elevation was computed using the geoid height.

    I guess the monument is not so new according to the data sheet.
     

    Attached Files:

  10. billvhill

    billvhill 3-Year Member

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    Can anyone see the OPUS solution, don't know if I uploaded it right
     
  11. Bill93

    Bill93 7-Year Member

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    So it is in the NGS data base. NEVER rely on a stamped elevation if you can get a data sheet.
    https://www.ngs.noaa.gov/cgi-bin/ds_mark.prl?PidBox=AJ7779

    But indeed there is some disagreement. I'd want more than 29 minutes of data.
    AJ7779* NAVD 88 ORTHO HEIGHT - 2338.2 (meters) 7671. (feet) GPS OBS
    Your OPUS report 2337.629 a little over a half meter different
     
  12. billvhill

    billvhill 3-Year Member

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    Yes, I'm on the monument as we speak.
    I'm using a tripod and also want to check if I didn't screw up an HI, if I get the same results, I can rule that out. I been on the point for about an hour. I have several occupations at the actual site about 3 hours long. This occupation on the bench was to just check my solutions vs a published monument, which I hoped would have been much closer
     
  13. MightyMoe

    MightyMoe 6-Year Member

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    none of that looks very good, the GPS elevation of 7671 feet on the data sheet was established using GEOID99. Then it was adjusted in June 2012 using GEOID 12B. The ellipsoid height on the data sheet is 2321.78, on your OPUS it's 2321.16 which is big difference, and now you have three very different elevations of 7668 (DOT), 7669 (OPUS), 7671(DS). I wouldn't trust any of it, I would first be very sure you gave the correct HI to OPUS using the diagram for your antenna.
     
  14. Jim in AZ

    Jim in AZ 7-Year Member

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    What makes you think your DOT is working on the same datum as NGS?
     
    Kris Morgan, JKinAK, Brad Ott and 2 others like this.
  15. Mark Flora

    Mark Flora Member

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    Do you have post processing software so you could confirm or check your data solving to CORS?
     
  16. Rankin_File

    Rankin_File 7-Year Member

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    2 METER FIXED HEIGHT ROD WITH A 8 MINUTE BUBBLE= ARP DETERMINATION IS CLOSE TO BULLET - PROOF.
     
  17. billvhill

    billvhill 3-Year Member

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    I had a 2 meter rod but the wind was blowing about 35 miles an hour and I couldn't get the tripod to set high enough to make it stable and the monument is on the the head wall of a canal that is running pretty hard. Just one of those setups that lower is better at the time.
     
  18. aliquot

    aliquot 6-Year Member

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    But OPUS is NGS.
     
  19. billvhill

    billvhill 3-Year Member

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    No I don't
     
  20. billvhill

    billvhill 3-Year Member

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    I'm not assuming that it does, but it seemed like a good place to start and check into since it is the nearest monument I could find and had an elevation stamped on it.
     

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