NTRIP Stream Conversion

Hi all,

Here in Australia, we have a free CORS network (AUSCORS), which is broadcasting in GDA2020, the latest datum, but the majority of projects I work on still reference GDA94. My question is, is it possible to convert an NTRIP stream, in real time, from GDA2020 back to GDA94 ?

Thanks in advance for any help !

Hi @Brocxen,

You can use the Custom coordinate system setup with the transformation from GDA2020 to GDA94. This can be done via 7 Helmert parameters. Besides them, you also need projection parameters. You can check them in the required coordinate system in ReachView 3 by tapping the info button.

And what is really nice coincidence is that our Custom coordinate system setup guide describes the exact transformation you require. You can read it here in our docs.

Let us know how it works for you!

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Oh, I thought I read that the project projection had to be the same as the projection for the corrections received from the ntrip base. Is that not correct? How does the RS2 know what projection the corrections are in?

The rover’s coordinates will be in the same datum as the base has, that’s how it works by default. But its coordinates can be transformed into another datum by applying transformation parameters.

Reach RS2 acting as a rover doesn’t need to know the base’s datum. It just applies GDA2020 to GDA94 transformation to incoming data. Indeed, if the NTRIP base has another datum, the outcome coordinates will be incorrect. But as long as you know your provider streams in GDA2020, everything is fine.

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I have followed the link you send to convert GDA2020 (connected to a GDA2020 Base) to GDA94. But the resulting coordinates look like the following:

Easting 6247432.385 m
Northing -7078016.390 m
Elevation 159.983 m

It should look like:

Easting 437xxx.xx m
Northing 8150xxx.xxx m
Elevation 168.528 m

Hi Brocxen. I followed the doco to convert auscors to 94 in z55. The Emlid doco has an error in the scale factor when entering the Scale factor for Projection it should be 0.9996 and not 0.9966. Give that a try

I’ll give it a try.

Also, what did you need to change for zone 55? The tutorial is for zone 51, I would need zone 50 and 52

This is what I have entered, pending the scale factor change mentioned.


Central meridian for 50 is 117… zone 52 is 129. Just google “central meridian for zone xx”

Thanks Noel

Aren’t the rotation suppose to be negative?


From Geocentric Datum of Australia 2020 Technical Manual v1.2

No, as it says at the bottom of your image, multiply by -1 for gda2020 to gda94.

:man_facepalming:
Thanks

Broxcen Did the scale of 0.9996 work?

Unfortunately not, so i am not sure what the issue is.

Hi @brocxen,

Please record several points in this custom CRS (GDA2020-to-GDA94 / MGA zone 50) and corresponding CRS without transformation (GDA2020 / MGA zone 50). Then, send us two resulting CSV files to support@emlid.com. I’ll check with the team what may cause such an enormous difference in the coordinates.

@noel, indeed! We’ll fix this typo.