NGS Survey Marker Not Matching

[ryans]

Greetings, just trying out my new RS3. I have an NGS survey marker not too far away where I can get just enough cell phone signal to get NTRIP corrections over the Internet from a site about 25km away (run by SparkFun I’m pretty sure).

I created a project in Emlid Flow, set the coordinate system to NAD83(2011) / UTM 13N. I then input the coordinates from the NGS datasheet as a point. Then I went out into the field, setup the RS3 to receive (and confirmed it was getting) the NTRIP corrections, and recorded a 60 second averaged point (albeit handholding the rod).

Unfortunately, the recorded point was ~1.5m away from what the coordinates gave on the datasheet. I’m guessing I must have entered the wrong coordinate or needed to convert, but I’m not sure exactly what.

Datasheet:

Coordinates in Emlid Flow:

Coordinates of recorded point on mark:

Inverse in Emlid Flow:

Any ideas?

[EBE111057 (Bryan Enfinger)]

I’d check with the Spark Fun people concerning the horizontal and vertical datum they are using for broadcast. If you are using any private RTN’s, you’ll need to verify what they are broadcasting

I’ve seen this so many times, wrong RTN datums not based on the NSRS vs published datums.

The attached indicates in UTM ZONE 13
UTM13_ 4,455,562.481 465,036.258 MT

https://www.ngs.noaa.gov/cgi-bin/ds_mark.prl?PidBox=AI3567

I’d also make sure you’ve selected the correct horizontal and vertical datum in Emlid Flow.

Another issue may be plate movement, we don’t have much in SC but I’m sure there’s some in Colorado

https://content.govdelivery.com/accounts/USNOAANOS/bulletins/2f82e09#:~:text=HTDP%20

[timd1971]

Like @EBE111057 said, your project coordinate system needs to be the same as the NTRIP RTN base.

I would assume they are using State Plate, NOT UTM. As you know, State Plane is used the most in the USA. Does SparkFun even provide a RTN service???

Try again with the State Plane CRS and see what you get. In the meantime, contact the RTN provider also for the correct info as @EBE111057 mentioned.

Should be off about 1.259843" at 25km out.

RTK FIX position
7mm+1mm/km
NTRIP stream from base <60km for Multi-freq receiver.

[jbonde002]

Looks like a classic NAD83/WGS84 difference. For ZIEBARTH there’s approximately a 1.398 meter horizontal and 0.859 meter vertical difference between NAD83(2011) epoch 2010.0 and WGS84/ITRFxx epoch current. These numbers look pretty close to your inverse numbers.

Is your NTRIP provider sending WGS84 (current epoch) corrections?

Poking around Sparkfun a bit they did describe setting up a basestation with ITRF14 coordinates.

Your output UTM coords are correct for ZIEBARTH in a WGS84/ITRFxx reference frame for the current epoch.

All above is just approximate to cm-level checking and not rigorously done.

[timd1971]

NOAA/NOS's VDatum: A tutorial on datums

[merryna.anggriani]

Hi Ryan,

Welcome to the community!

It’s important to ensure that the datum used for both the base position and the NTRIP correction are aligned.

I’d also recommend double-checking the correction data broadcasted by your NTRIP service.