Best procedure to check a known Geodetic Mark?

Disclaimer:
I am NOT a surveyor nor claim to be. I am not compensated in any way to impersonate one either.
It’s all for a great learning experience here to be utilized in other fields of interest. If I decide to become a registered land surveyor, I will obviously take the proper route. ; )

Using the website below, I have located some Geodetic Marks in the area that have GPS and Vertical Control. United States.

Obviously, the NGS Data Sheet has all the information needed. i.e. NAD83 position, NAV88 orthometric height, ellipsoidal height, geoid height, etc.

I have (2) Reach RS receivers (BASE / ROVER) and all necessary equipment (i.e. bipod, tripod, data collector(s), FieldGenius, etc.

I know I can set manually on that known point (convert NAD83 data sheet position to WGS84 LLH) in ReachView and collect points in this area within the LoRa radio range or NTRIP, CORS etc. But using LoRa as convenient.

What is the proper procedure to measure this Geodetic Mark to compare what I get and what was recorded in the NGS Data Sheet?

From what I understand, OPUS does not work with SINGLE BAND receivers such as Emlid Reach RS. But does with the RS2.

Also, simply, what is the VERTICAL ORDER? i.e. first, third, etc?

Thanks all!!!

National Geodetic Survey Data Explorer (noaa.gov)

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Hi @timd1971,

If I understand correctly that you’d like to collect points with absolute accuracy to compare them with the Geodetic Marks, you will need to place the base on a known point. There are the following ways to do it:

  • If there is a known point nearby, you can place your base on it

  • If you have access to an NTRIP caster, you may average the base position in Fix

  • As you noticed, OPUS can’t process logs from single-band receivers. However, you can upload raw data from Reach RS to the NRCAN PPP. Please note that the service provides only around 30 cm accuracy for single-band receivers.

If the coordinates of the base are saved in NAD83 LLH, you can collect points with the rover in NAD83 + NAVD88 height in the ReachView 3 app. To learn more about the workflow, you can explore this video guide.

Could you please clarify what do you mean by the vertical order? It will help me to provide the most relevant answer.

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Here’s NGS’s datasheet explanations

https://geodesy.noaa.gov/datasheets/SurveyMarks_FAQ.shtml

Basically, vertical order is the vertical accuracy of the of the mark. For example, in Vertical Order “First- Class II” accuracy, the mark elevation has been established by differential leveling technology, i.e leveling of the mark from an established benchmark. This is the second most high accuracy classification. NGS does differential leveling to define the orthometric heights of the mark to further define the geoid- orthometric separation (geoid model heights).

Using your GNSS receivers, you are determining the actual ellipsoid height of the point. Using any geoid model separation values for the area, you can then determine the orthometric height, i.e. rough ground elevation. The orthometric heights in itself is the model of the ground surface which takes into account gravity values (deflection of the vertical).

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Thanks for the vertical order information… much appreciated.

Besides differential leveling being the second most high accuracy classification… what is the first?

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Same, just different accuracies and methodology of differential leveling. Leveling the mark and GNSS observations of ellipsoid heights determines the geoid-ellipsoid separation. Using this methodology for a network of control marks establishes the geoid model for the area.

Here’s just one of the methods of determining the geoid model

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https://geodesy.noaa.gov/GEOID/

Great information here, this has always fascinated me. We saw a gravity observation crew about 15 years ago performing observations in the area of Haile Gold mine. I learned a lot just talking with them. Using this method they can determine the locality of gold as it’s mass is greater than the surrounding geologic area. Also determining the deflection of the vertical in the area. Pretty fascinating stuff ! !

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Yes m’aam.

But before I do, I only have ONE known geodetic mark provided by the NGS. I want to “check” this point against the NGS data sheet to make sure it is good before proceeding further in case it was disturbed etc.

So I guess I am wondering what the proper procedure is to “check” the ONE known geodetic mark I have?

No CORS, no NTRIP etc. Just BASE & ROVER.

My guess is this is where a surveyor or other methods come into play? i.e. traversing / backsighting / foresighting using total station from another known geodetic mark that could be very far away?

Hi @timd1971,

If the base position is averaged in Single, you will get relative accuracy only. To determine the coordinates with absolute accuracy without corrections from NTRIP, you can use the PPP technique. For PPP, you will need to place one of the receivers above the point, record a raw data log for at least 4 hours and upload the log to the NRCAN PPP. PPP services need some time to get precise orbits, so you may need to wait for a while before uploading the data to get a better solution.

I can hardly comment on the accuracy that can be achieved with a total station since we haven’t conducted such tests.

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The only way to check the NGS passive mark is to occupy and log an observation of at least an hour and PP. Then you can compare your “check” observation to the datasheet information.

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Thank you!

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Yes, a long valid PPP session and correct transition of coordinate system would be my goto solution.
But getting from A to B is so different around the globe. But with the right tool and work order, some final Q&A should yield credible data

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