Low Cost, High Performance RTK Module from Tersus


We are a new company in the market who make high performance and low cost RTK module for drones.

Please take a look and if you are interested, we can arrange a demo for you.

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could you kindly explain your understanding of relative vs. absolute accuracy in case of GPS unit ?


if the base are in placed in your roof( you don't know the location at all), then the relative accuracy is still within 1cm. but if you have some tools to get the precise geo information about you roof antenna, then the absolute accuracy is within 1cm."|

I am interested also on the demo. However, it is too far away from my home in Indonesia. Could you share video of the demo on youtube? Thank you.


since you can receive diff and RTK corrections over the Internet

you can setup fixed Virtual Base Station to setup fixed Ground Control Point

and to use this GCP as diff corrections broadcaster over radio to GPS unit embedded into smartphone, connected to drone controller to correct

GPS data extracted from NMEA sentences against virtual GCP diff corrections.

Let me know your opinion.

I would recommend that you support the RINEX format logging for your unit. (https://igscb.jpl.nasa.gov/igscb/data/format/rinex210.txt ) for the purpose of being able to get an exact fix of the unit used as a base station. Here in the US we have the OPUS service (http://www.ngs.noaa.gov/OPUS/)  that will give precise coordinates from a log file that from a base station that has spent 2 to 3 hours on the same spot by post processing the logged data. With this ability your product could compete with much more expensive systems. Without this ability your system can't be used for real world problems that require the ability to obtain a precise position of the base station location after the mission has been flown. Such as getting volumetrics from quarry stock piles at locations that don't allow for surveyed control targets to be placed in the work environment.




I am approached by manufacturers of high-precision Ublox chip based GPS units, claiming 5-10 metres accuracy due to ionospheric error.

If remote service can postprocess GCS raw data to provide geodesy grade
1cm accuracy for the ground based station so why the number of GCS is so limited and not grows into global high-aacuracy GCS network
and placing raw data output GPS unit at geodesy grade GCS point, one could
build high-accuracy RTKLib based Rover.

Basing on your experience with RTK modules, tell me if GCS and Rover should not generate 3DFix based on the same constallation and HDOP and PDOP should not match to get GCS and Rover offsets to match either.


My understanding of Ublox units is they are only L1 type systems to get to centimeter type measurements requires a L1, L2 GPS capable units. That is why I was recommending logging the positional information because this system is L1, L2 which should increase the ability to get higher accuracy positional data.


Totally agree with Robert, everyone is focusing to get RTK fix which is very important for navigation but for mapping what is very  important is to get cm precision to the positions from where the pictures has been taken and this can be easely obtained if we have a GPS (even L1 GPS only is enough) that is logging RINEX data using a survey postprocessing software.

Currently no GPS unit built for UAV's doesn't support onboard RINEX logging and to hack a few thousands $ survey grade GPS receiver (in order to reduce weight) doesn't look like a good choice.

Robert, Cioro

It's great to know what requirements is critical for field operation. We are working on logging the rinex in PRECIS L1 and L2 observations. Currently we plan to support the PRECIS UART output soon, end user need to attach a device/ PC to receive/log the raw data.

In our new L1 only platform PRECIS -2 board, we have 32G SD card on board . So it's easy to log the raw data for several days.



Tersus-gnss Team


Thank you for your feedback.

Currently we're mapping some area with swamps using a multicopter. I think you can imagine what kind of effort we spend in getting the GCP's.

So as soon as you get RINEX raw data out from your receiver and stored it on board, please make the announcement here or on your website.

It is also important to store data on board (128 Mb is enough space to store 10-15 hours of observations at 0.5 sec recording interval) because RINEX raw data stream have to be perfectly continuous (even one missing epoch can affect the postprocessing). You can store the data directly in the onboard memory and the user can download the RINEX files after each landing through BT/USB cable/WiFi. Also please consider that in order to get a good carrier phase data you need a high quality antenna and good filtering (which can be acquired from the market).

We are very close to hack a GPS Magellan Promark 500 to install it on multicopter but because of the considerable weight (>600g) we had to build another platform to support it so we postpone the project.

Is there any advantage to logging in RINEX format directly by the RTK receiver than logging in more compact raw data binary format and later convert to RINEX on a laptop?

I didn't mean to mislead, there is no need to use the RINEX format for the actual real-time logging. A more efficient binary format would probably make more sense for the actual logging. As long as this format can then be converted to RINEX for post processing.   


Of course that binary format is much less memory consumer, this is how all the professional GPS manufacturers do.

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