How to set the antenna height for RTK?

Adam,

I’m glad to hear that! :slight_smile:

And sure, all your questions are welcome.

Hi everyone,

I have question about the new version for emlid flow, and is referent to the antenna high and CSV.

If I make the initial position of the base in Average Single, and I also enter the height of my Base instrument. Is this instrumental height or the new height calculated from the height of the instrument present in the CSV file?

Hi Bernard,

You can see the base’s antenna phase center coordinates in the CSV file. So, the Base ellipsoidal height from CSV is calculated as the Ellipsoidal height of the base marker plus antenna height.

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Hello @julia.shestakova

Is the APC (mean) shown in the image the AVERAGE of L1 and L2 of the RS2/RS2+/RS3 which is 134mm? So L1 is higher than L2?

Thank you!

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Where is this documentation for the separate L1 & L2 offset measurements please? (I understand to plug in 134mm for the offset for SIMPLICITY, but would like to know the actual L1 & L2 measurement specs as are generally shown in most antenna diagrams (see example below); if 134mm is L1 & L2 averaged for APC or if APC to L1 only).

Thank you.

image

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You can download a copy of the NGS antenna calibration. For example, the RS2+ calibration is here:

EML_REACH_RS2+

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thank you @dpitman

I haven’t delved into the calibration aspect yet. But do you happen to know what each line refers to here exactly? Are they (4) samples / results of YXZ (NEZ) in mm basically? Maybe phase center accuracy is about 2mm± for the RS2+? Do not see these details in any specs. Yes, very minimal tolerance of error, but still curious.

Thanks! Much appreciated!

-0.98 +1.92 +134.92 NORTH / EAST / UP
-0.44 -0.06 +137.10 NORTH / EAST / UP
-0.98 +1.92 +134.92 NORTH / EAST / UP
-0.44 -0.06 +137.10 NORTH / EAST / UP

Tim,

I think that calibration shows the L1 and L2 calibration for GPS and GLONASS satellites. The first one is GPS L1, the 2nd one is GPS L2, the 3rd is GLONASS L1 and GLONASS L2 is the forth.

See how the first and third, and 2nd and 4th are very close to each other?

So, Emlid basically says to use the figure for the L1 frequencies.

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Thank you Dave… can always count on you among a few others here that really know their stuff
; )

Not sure I follow you here?

Figure?

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135mm vertical offset is the L1 adjustment. The L2 is approx. 137mm

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OK, thank you for the clarification! I think your prior reply is reversed then for L1 & L2?

This is why I wish EMLID had a diagram/drawing of this to keep it simple…

… so if I follow you correctly, L1 APC point is higher at 137mm±, and L2 APC point is below at 135mm± based on this particular calibration.

So the typical 134mm offset provided by EMLID is within 3-4mm± tolerance. Obviously the calibration data is even better since it is provided. I would assume these would be different between different receiver builds also, but the tolerance of error is pretty low and within their specs.

Thank you Dave! :grinning:

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Yeah, I might have the L1 an L2 reversed. The calibration document is minimal in it’s definitions. If we assume that L1 is listed first, then you are correct.

Agreed. And even within a single receiver, there could be changes over time I think as being jostled around, heated and cooled, etc. can effect the magnetic field, I bet.

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Hi there,

In Emlid Flow, we apply the offset to the physical antenna position—0.134 m. The difference between it and the APC coordinates is much smaller than the precision of the RTK technology. So, these settings provide accurate coordinates in RTK.

At the same time, Emlid Studio automatically applies antenna calibrations from the ATX file Dave shared.

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FYI:

EXPLAINS ANTEX and ANTINFO formats.

https://files.igs.org/pub/data/format/antex14.txt

https://geodesy.noaa.gov/ANTCAL/documents/format.txt

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Per calibration file, you were correct to begin with @dpitman , thank you! so Emlid just uses 134mm for L1.

G01 (GPS L1) -0.98 +1.92 +134.92 NORTH / EAST / UP
G02 (GPS L2) -0.44 -0.06 +137.10 NORTH / EAST / UP

R01 (GLONASS L1) -0.98 +1.92 +134.92 NORTH / EAST / UP
R02 (GLONASS L2) -0.44 -0.06 +137.10 NORTH / EAST / UP

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Something that I and others have pointed out is that when you do postprocessing in Emlid Studio it doesn’t use the manually entered coordinates from Emlid Flow.

You have to set those values again in Studio, or drag a POS file into the box. For example I correct my base station using a CORS station, and then drag that single position POS into Studio to set the base coordinates.

The problem is most users don’t seem to know this and assume base coordinates are retained from Flow to Studio!!

I think it should be made clear in Studio what is going on and maybe prompt the user to put in coordinates or choose a POS file.

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So in the case of base coordinate averaging, do you enter an antenna height of zero?

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Hi @daygeckoart,

Thank you for sharing your feedback on this. It’s a good point, and we’ll think about what we can do to make it clearer in the app.

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Hi @kdoherty,

Good question. Thank you! Technically, you don’t need the antenna height in this case. You’ll already have the APC coordinates after averaging, so they will be used for calculations in RTK.

However, I still recommend you enter the actual antenna height. This way, the app will calculate the coordinates of the point on the ground. It’ll allow you to use the same point in future surveys and get consistent results.

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Thanks for getting back to me. In our case we are mounting an RS2 on the roof of our facility to serve as a permanent base, broadcasting corrections indefinitely. We plan to average position only once, and don’t plan to move the unit after switching it to broadcast over NTRIP. It is not straightforward to me how to estimate height above ground as I cannot access the terrain below the building, or I’m not sure if I should consider the convex hull of the building the ‘ground’.

For my application, what is the best practice for parameterizing antenna height in Emlid Flow? Am I correct in my understanding that setting an arbitrary antenna height of the base won’t influence the quality of corrections the rover will receive?