How Do I Create a (new) Known Point?

[dronemapper23 (Eric T)]

I recently purchased two RS2+ receivers. I want to use them to record the locations of my GCPs. So far in my research, I think I’ve found that I need to place the base station over a known point. Then connect the rover to the base using LoRa radio.

My first question is: are known coordinate points listed publicly anywhere? If so, where?

Next, I think I’ve read that I can create a (new) known point using one of my RS2+ units and a procedure called Static Processing? And this requires post processing in Emlid Studio?

There is a tutorial on how to do this, which states I need a RINEX observation file from a CORS, a RINEX observation file from a local base, (which I assume is my RS2+?), and a RINEX navigation file from a CORS or a local base. I am hoping someone can provide me with step by step instructions on how to acquire these things? Or that someone at Emlid can create a tutorial on how to do this?

In regards to the RINEX observation file from a local base, I assume this means I need to log (record GPS data) for a certain amount of time using one of my RS2+ units? I think I’ve read this takes a minimum of 15 minutes or how long should I log GPS data on my RS2+ to create a usable RINEX observation file?

After I have these three required files, I can use Static Processing in Emlid Studio to create my new Known Point? Once my new Known Point has been created in Emlid Studio, I can then transfer or export it back to ReachView 3 or my RS2+ base unit, then connect my rover RS2+ unit over LoRa radio and collect my GCP locations?

It would really be great if Emlid could create a video tutorial on how to do all of these things?!

Thank You in advance!

[dpitman (Dave Pitman)]

Here is some documentation to help get you going. You’ll likely still have questions, but with a better understanding.

https://docs.emlid.com/reachrs2/

https://www.youtube.com/@Emlid/playlists

[snillor999]

Not sure where you are located, but I can speak for the USA. Also, I am not sure what type of accuracies you need and if you are using this commercially that requires you to be on a specific horizontal and/or vertical datum. But I’ll try and answer your questions …

Question 1 - Where to find known coordinate points ( or establish your own)
If you are on an existing project that has been established then I would ask your client to provide you with the project site control.

If you are just trying to establish your own control then there are a few options… NGS has a GIS map of their control monuments and also OPUS Shared solutions at NGS MAP. Then you can establish control on your site by doing a static mission running a unit on the NGS control monument and another unit one of your site GCP.

City / State / County GIS normally have control monuments that can be found on their websites.

You can also set up your GPS base and record raw GPS data and upload it up to NOAA’s OPUS website and OPUS will give you coordinates. The longer the session the better. For example, the Corp of Engineers in my district require a 5hour session. You can get by with as little as a 20 minute GPS observation, but you are trading time for accuracy.

You could collect some raw GPS data on one of your GCP, then could download CORS data and use the CORS Station as your base and use the published coordinates of that station for your base and use Emlid Studios to run a static mission with your GCP raw data.

There is something called PPP ( Precise Point Positioning ) which just uses your GCP Raw data (without a base station) to compute your location. I have never done this and I assume is one of the least accurate methods and I assumed its mainly used in remote areas.

NTRIP will give you RTK quality precision with the corrections coming over the internet instead of over the radio from a local base. NTRIP range drastically in prices. Some states like NY DOT have a free service, North Carolina has a $500 lifetime license for up to 2 licenses, or there are subscription based that can be upwards of $2k a year.

Question #2 ( Using Emlid to Process Static Data)
Yes, you can use Emlid Studios to post process static GPS data. Normally this is done by having a unit running on a known base and another unit setup on an unknown location at the same time. By collecting simultaneous raw GPS data you can upload the known and unknown Rinex data into Emlid Studios to compute a position on the unknown. There are other programs too that can do this. Observation time depends on distance between the 2 points. 15 minutes may give you what you want - I would probably do longer, but I’ll let you do your own testing.

And once you get the ‘Known’ position on one of you GCP you then can input those coordinates into ReachView3 as your base coordinate and broadcast a correction to your rover while you collect your other GCP with the Rover with RTK precision.

Hope this helps
too and is not limited to Emlid Studios.

[dronemapper23 (Eric T)]

Thank you for your response. It was very helpful. I will have to do some research on how to find known control monuments in my city, county, state (Reno, NV, Washoe county).

My next mission will be to learn how to access and download RINEX observation files from my local CORS station. I think I can do this on CORS Map

My local NTRIP is $600 per year. Funny thing is I bought the second RS2+ receiver because I thought it would eliminate my need to access NTRIP, but I guess I was misinformed.

Your last answer under Question #2 says I need to have a unit running on a known base, but I was hoping it was possible to use Static Processing to create a new Known Point without needing an existing known point or having to pay for access to NTRIP. Based on your answer, I guess this isn’t possible.

Based on the information you provided I think my best option is to use my local CORS station as my base and Emlid Studio to run a static mission with GCP raw data from one of my RS2+ receivers.

Thanks again for responding to my questions. I really appreciate it!

[snillor999]

@dronemapper23 I believe I threw a ton of info at you and I did not explain well, because it looks like I confused you on some things. I almost think you were better off before reading my post. I’ll try again …

First, you were originally correct in thinking the second RS2+ unit would eliminate the need for NTRIP. NTRIPs are very useful when you only have one unit or would like to save time by not having to set up a base. With a NTRIP you drive to the site, turn the unit on, connect to the internet and NTRIP, and BAM you have RTK corrections and can go straight to locating your GCPs. Downside with NTRIPs (unless you are running your own) are they can be expensive, you cannot control the corrections you receive and may or may not be on the datum you need, and the NTRIP bases could be further away - reducing accuracy, Upside is - they are quick and easy (as long as you have access to the internet at your site) and some services allow for you to receive a correction from a network of NTRIP base stations.

I confused you under my “Question 2”, because If you have 2 units you do not need NTRIP and if you run static you absolutely can establish a new known without the need for NTRIP.

As mentioned you can use the CORS station as your base station and a run static mission to get a ‘new known’ on-site.
You could also run static by placing a unit on a NGS or City/County Control Point and another on-site to get a ‘new known’ on-site.

[dronemapper23 (Eric T)]

@snillor999 Great, that really clarifies things for me. Now I just need to learn how to use my local CORS station and the static processing procedure so I can create a new known point that is on site for my base. After that I will connect my rover to it so I can collect my GCP locations.

I understand the longer I record (log) data on my base during the static mission the more accurate my new known point will be.

Thanks!!

[snillor999]

Also, remember you have the OPUS option. You just upload your GPS Rinex file, select your antenna model, and set your rod height and the website will use I believe 3 CORS and computes you a new ‘known point’ with a report regarding positional quality. This will eliminate you having to download your CORS data manually and processing the data yourself.

Even if you do decide to manually download CORS and post process your data, I would still upload to OPUS or ‘tie’ into other known survey control points for added quality control.

Best of luck!

[dronemapper23 (Eric T)]

Ok, I’ll look into OPUS as well.

[svetlana.nikolenko]

Hi Eric,

If you’re from the USA, OPUS is a really good tool to establish a known point for your local base. If you haven’t seen it yet, we have a guide about processing Reach logs in OPUS.

Overall, I agree with all the comments above. There are plenty of options to find precise coordinates for your point. And you don’t usually need a subscription to NTRIP if you have your own base. But if you have it, by any chance, it’s the fastest way to establish a known point for your local base on a site.

Good luck with your research! You’re always welcome here with any questions.