Third party application

Hi all,

I am using one RS2+ for collecting georeference geophysical data with a third party software.

The system is communicating fine via Bluetooth and working fine with RTK corrections as specified in the recommended set up.

I am very satisfied with the horizontal resolution but I rarely seem to go below the 10 cm difference vertically from local topographic survey after transforming the data using Ordnance survey software.

I have several questions:

1)Is that normal or I should have only 2 or 3cm off in elevations?

  1. Would having a base and a rover improve significantly the vertical precision from only one rover using NTRIP or this only required when too far from a base station ?

  2. is it possible to log continously in local transformation and local datum ( like when surveying with emlid flow) AND at the same time getting NMEA strings to the third party software via Bluetooth?

I hope the last question is not too confusing.

Basically I am frustrated with the fact that we can’t get directly local elevations into the third party app…


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The Antenna Phase Center (APC) to ARP is ~.134m so perhaps it’s just an antenna height bust. If you are using a fixed height 2m rod, Emlid Flow will automatically add the APC offset for a total of 2.134m for the antenna height. Using third party software, there is a good chance that you need to manually account for the APC to ARP measurement and put in 2.134m versus 2m. Hopefully, it is that simple.

Also, yes to your last question.


Thanks Zac, it’s very much appreciated especially the last question clarification.

I just need to retrieve the logs after acquisition?

The rover is on a pole but no settings are given so he thinks it’s ground level and we correct after however I have read that the ACP in the forum is either 134mm or 137mm depending on the band.

How do we know which band is in use?

Not that 3mm would matter but it makes sense that the 134n137mm are not taken into account since we do t use the Emlid flow offset preset.


Hi Brice,

I agree with Zaz. It looks like this 10cm vertical mismatch is related to the antenna offset - 134 mm in the case of RS2+. It’s added automatically in Emlid Flow, but you need to set it manually in case of 3rd-party software. The offset to the L1 and L2 phase centres are indeed 134 mm and 137 mm.

You can use the offset to the physical antenna position (134 mm) as in Emlid Flow. The difference between it and the APC position is smaller than the precision of RTK. It won’t affect the accuracy.

Using your own base or an NTRIP service are just two different ways to work in RTK. Their accuracy is similar.

Yes, it’s possible. However, position logging will provide a log in geographic coordinates, not projected coordinates. What would you like to use these simultaneously for? Maybe I can suggest a workaround for it.


To be more precise based on antenna calibration if your software allows entering NEZ:

-0.98 NORTH +1.92 EAST +134.92 UP

-0.44 NORTH -0.06 EAST +137.10 UP

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Hi Tim,

These offset values are in mm if I understand correctly?

I get the point from Kornel that these tiny offset are below RTK precision but it’s is great to know these values.



Thanks Kornel for clarifying all the queries and sorry about the late reply.

My issue is that I can’t get the most of the altitudes value coming inside the third party software as it gives the orthometric height from the WGS84 instead of the ellipsoid height and I would need to transform. all the elevations for each profile recorded…

If I could record the projected Irish ITM Malin Height (OSGM15) elevations continously wherever I push the cart in parallel that would be great.

An issue would be synchronicity with the third party software recorded profiles but at least I would have the correct local elevations directly to either try replace the elevations or create a DEM to work with.


You probably should reach out to the third party app support with the details of Emlid.

The software should have fields to enter Antenna Height, Antenna Reference Point (ARP), Antenna Phase Center (APC)(NEZ L1 L2 or just L1) and also for GEOID along with your coordinate system. The GEOID will allow your orthometric heights in relation to Mean Sea Level (MSL) in real-time hopefully, otherwise you will just Ellipsoid height based on WGS84.

You could use Emlid Flow with the GEOID plugged in to test and compare. Just enter ARP (bottom of emlid to point of observation, i.e. 2M pole) as Flow automatically takes into account the APC.

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Hi Brice,

We use the EGM96 geoid for NMEA GGA. This message includes orthometric heights and geoid undulation in relation to EGM96. There is no way to change the geoid, but yes, the values can be transformed in the 3rd-party software.

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