Fundamentals of Coordinate Reference Systems and RS+ .... Help

Hi all. First post so apologies as it is a long one. I am just unable to find this answer independently.

I have a drone business in remote NW Australia and purchased 2 x Emlid RS+ to capture accurate Ground Control Points. I have only used a borrowed Trimble previously which had Satellite RTX positioning and would also capture points in whatever CRS I desired….I thought I knew what I was doing. Knowing some of the terminology and processes does not wisdom make!

I really only have 2 workflows I need to get right, but I am noticing that I don’t have a grasp of some of the basic fundamentals around Coordinate Reference Systems to know if I am capturing the points correctly combined with a little confusion around the Reachview 3 workflow.

I need to either
a) Position my base over a known State Survey Mark (supplied in GDA2020) or other known point and capture GCP’s with the Rover, output to be in GDA2020 or;
b) Position my base using an NTRIP transmitter for RTK fix and then capture GCP’s in GDA2020

I understand how to connect Base/Rover etc. Where I fall down is the coordinate system and how to leverage the data I need from Reachview 3.

My questions are

  1. What CRS does the Emlid RS+ display when just using satellite for a fix? Is it WGS84? Which EPSG code?
  2. What CRS does the Emlid RS+ display when using NTRIP RTK? Is the CRS of the NTRIP station relevant?
  3. If I start a project on my rover using Reachview 3 and select coordinate system as GDA2020 then will it automatically get that correct regardless of the base stations CRS fix, or
  4. Is the only time I can select GDA2020 as the CRS for point capture when I have manually entered a GDA2020 point in the base?

Can anyone share a workflow for positioning the base over a known point with a known CRS and then obtaining your marks in the desired CRS, same or otherwise. No doubt I’m missing some basic fundamental.

Thanks in advance for anyone who can help.

Yep, WGS83. Not sure of which epsg code.

It displays the coordinate system of the NTRIP, so yep, the system of the ntrip is everything.

While you can select it whenever, the only time you get the right position in GDA2020 is when your base/ntrip is also in that setup.
For a local base that means that you have set on a point where the coordinates are supplied in that particular system.

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Thanks @wizprod, appreciate the response. I sort of knew but just needed some confirmation.

So if I needed my outputs to be in GDA94 for example but I only have a known GDA2020 point, the easiest way would be to convert the known point to GDA94 then set the Reachview3 project to GDA94 also. Ultimately, base and receiver must be on the same coordinate system. There is no automatic correction?

Hi Jeremy,

Agree with Christian, but I want to add some details:

  1. When Reach RS+ works in Single, it calculates the position in WGS84 (EPSG:4326)
  2. When the unit is in Fix, it calculates coordinates in the datum of the base/NTRIP. You can also choose a projected CRS based on this datum in the ReachView 3 to get the projected coordinates.

There is no automatic correction?

There’s indeed no transformation applied in between. So, converting the known point to GDA94 is the most straightforward way to get all points in the same datum. You can check our base and rover setup guide for Australia for a bit more details.

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Thanks so much. That clarifies it perfectly for me.

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