Export RTK-corrected GPS data to RS232 serial port


as I understood many terminals got a RS232 interface, e.g. the Amazone Amatron4. The device is able to import the GPS data from that serial port. I wonder, if AGOpenGPS preprocess the GPS data to be fully RTK corrected, could that data be exported to such a device and therefore get full RTK precission?

Also could be interessting for the Trimble GFX750 - which also has a RS232 port - to avoid that huge extra licenses they only ask for RTK corrections.

Thanks for your ideas and comments.

Your GPS/GNSS “Rover” (tractor receiver) does all the RTK position calculations from the correction data it receives from the “Base” (stationary receiver).

The GFX is a Terminal, it requires correction data to be sent from its Reciever. In order for it to accept RTK correction data the Reciever must be “RTK Unlocked”. There is no way around this, its how Trimble makes fat cash.

The GFX 750 only uses a Trimble external receiver, but I cannot find any documentation as to what message format it is using. But it is most likely Trimble TSIP or GSOF.

Having a 232 port does not mean the data that travels over it is compatible with any device that has a 232 port.

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Maybe this helps?

I think he is hoping that he can plug any GPS receiver into his GFX and have it work.

This is the exact reason why AOG is becoming such a desired platform. With AOG you are free to use any receiver you wish that outputs standard NMEA. The whole system costs less than Trimbles $3500CDN unlock, or Deeres $9500CDN unlock.

I know a lot of farmers who want to try AOG but since it is not plug and play, they will never use it.

If you kept your Ez Guide 150, you can do what he described above. Its the only Trimble that lets you autosteer off NMEA. I also wrote a converter for the 150 for TSIP from NMEA, cause on this unit they are very similar.

I am currently trying to make an emulator for the 252 receiver. But its much more complex so no ETA.


Yes indeed, there is a post in a german forum:

Eine Antenne für Cerea und Amatron3? - Empfänger OEM - cerea-forum.de (cerea-forum.de)

It exactly discusses the useage of a single antenna with Cerea (instead of AOG), but one farmer describes that he has the antenna connected to Cerea and outputs through serial cable (via USB) to Amazone Amatron3. So I guess it should work the same way with new Amatron4. So you can make the Amatron RTK ready with little costs in the end. So how I came about the idea to use it with Trimble. In Germany the costs from Trimble RTK-Unlock are in the range of 4k€ net plus either a cellular modem (1.5k€) or a Bluetooth connection module (software unlock, 500€).

On the other side, I assume that the tracking and guiding software works the same way for RTK and non-RTK corrections - just with the fact that the input signal is more accurate. Am I right? Or are the algos behavior actually changing when the software knows about higher precision?

Ok lets split this in four;

One is running the trimble guidance off 3rd party receiver. This currently will not work. RTK or not.

Two sending the implement NMEA from an F9P or Emlid. If the implement accepts NMEA 0183, you will need to know what talker code, and sentences are required. This will work more so with the highly configureable f9p.

Three is sending nmea to implement from gps used with agopen. Yes this will work if the implement is compatible.

Four is corrections. The F9P can use trimble RTCM3 corrections, but not the other way around unless you inject 1008.

Its well worth the time to figure out RTK outside of the big manufacturers, but it does involve a lot of reading forums like these.

The corrections increase the accuracy of the final computed position of the antenna.
If you change from WAAS to RTK, it usually involves recalibrating your steering again. Its not just a change on or off and it magically drives straighter.

But once you go RTK and its all tuned up you won’t want to operate without it.

Thanks for those insights.

I think it is understood that Trimble blocks all workarounds…

But coming back to point 3.
When AGO is sending the NMEA data to the implement, can the NMEA data “be sharpened” with RTK correction? As I understood RTCM can transport observed GPS L1/L2 plus in additional fields RTK information. So the target would need to extract this information and pre-process the data, correct? In the end it would mean that in my case a Amatron4 terminal may be able to receive the data through serial port, but not making use of RTK information inside the message packages? Correct?

As I understood the inject 1008 is just to pretend the data was coming from a original Trimble antenna?

Sounds like you have misunderstood the task of AgOpenGPS and the GNSS receiver.

The GNSS receiver may obtain RTK accuracy if RTK correction data is provided to this receiver. AOG can receiver the RTK correction signal from internet (NTRIP protocol), originating from some GNSS base station. The GNSS receiver makes use of this RTK correction data to obtain a very accurate location info. The GNSS receiver sends this location info to AOG as an NMEA data stream. AOG then calculates tilt compensation if the GNSS receiver does not do it (like a u-blox F9P).

Your Amatron is happy to receive NMEA at RTK accuracy from your GNSS receiver. Amatron4 does not need to work on this signal at all (it is not able to make tilt compensation calculations, hardly even needed).

Your Trimble GNSS receiver is the weak link. If it isn’t providing RTK accuracy, you would have to swap it with another GNSS receiver.

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Just like @NorthernFarmer says. RTK calculation is done in the receiver before position data is sent out.

Satellites—>Reciever+correction(WAAS, RTK,RTX,Omnistar)——> position output data——> guidance / implement rate——> navcontroller ——> Steering output.

The part where everything really starts getting confusing is position output data.

There is different communication layers; hardware - the physical cables and ports
Communication Protocol - rs232, tcp, udp, spi, i2c, wifi, CANBUS
Data protocol - NMEA, NMEA2000, RTCM3, RTCM2, CMR, CMR+, GSOF, UBX, TSIP

And there are many many more. Also there are different configurations and settings in each that will cause no communication. Some can be mixed others cant.

It seems like a lot at first, but all follow a standard and most can be read about.


Refering to that chain:
Satellites—>Reciever+correction(WAAS, RTK,RTX,Omnistar)——> position output data——> guidance / implement rate——> navcontroller ——> Steering output.

Does this mean for AGO that the RTK correction signal goes the way like that:

RTK Base → Internet → Mobile Phone connected w Bluetooth to AOG device → AOG device → F9P / Ardusimple receiver → merged with GPS data → result sent back to AOG?

Then I was wrong, I thought the AOG device is merging the correction data to the received GPS data. Okay, so I need to re-think a few aspects clearly.

Yes you are correct you can route your corrections through AOG to the ardusimple.

Or you can leave AOG out of it go…

Base–>loraradio (or any other data radio)–>Rover(ardusimple or any other F9P variant)

Lots of valid ways to skin this cat.

You do not need to use Ntrip if you have your own base, you can use the raw RTCM corrections.

The absolute most accurate setup will be the one with the closest base, and the least link latency, and the least extra data to be sent. Like a local base with a local radio sending RTCM directly.

But cell still works pretty good i was using my friends base 30km SE of me over cellular and I had 1.8" accuracy. If I use the local base in my yard over Lora radio it really holds the line incredibly well. I use Lora because then there is no extra network or caster fees.

But you must send corrections for all constellations you are using in the rover. If the rover is using all constellations, but you only send GPS corrections you will only fix on the available GPS satellites at the rover. The more satellites available to use the more robust your signal will be in challenging territory like hills and trees.

I live in Alberta so I always choose GPS, Galileo, Glonass and Beidou.
QZSS does not help me in any meaningful way its always way too low on the horizon.

Galileo is probably the best system, they have the most accurate clocks onboard, and are heavy into the L5 signal. Currently the most sophisticated satellites civilians can use.
GPS and Glonass are basically Trimble clones of each other, but I see Glonass more frequently with better signal this far north.
Beidou is helpful but if you can only run two or three this one is the one to leave off.

You can use one base for unlimited Rovers.

Can AGOPENGPS export its gps data out over usb to a rs232 adaptor and into my pro 600 monitor? Would be an easy way to have section control while using AGOPENGPS.

Do you need bit rate conversion from the existing AOG input to the output for your pro 600 monitor? If not, why not use a serial port splitter? Don’t like any extra burden for AOG implementation if there is an easy and free alternative already.

I found ttl to rs232 adaptor online. Maybe I could have an output off my uart1 interface on the simplertk2b and then go to my pro 600 that way and skip the agopengps computer. I havent seen anything online about bit rates needed for the pro 600. I have found it needs 9600 baud rate and Nema settings of GGA 1hz


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I got two of these: https://www.ardusimple.com/product/xbee-to-rs232-adapter/

Haven’t tested out yet, but should be able to dump out NMEA from F9P UART, sits on the XBee socket.

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You can set the baud rate on the Pro 600 input to anything you wish. I have mine set to 38400 baud right now for seeding, currently getting NMEA from my John Deere receiver. One problem is that the GPS coordinate the Pro 600 receives is 30’ in front of the actual drill. Would be nice if AOG could translate the GPS back to the toolbar position (which is already done for on-screen drawing of the toolbar) and then synthesize NMEA for that.

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Would one of these be able to hook up to the uart and dump out the nema? Little cheaper and I can get it faster haha


Yes, that could be wired to the output of the f9p board.

Even something like this,

max 232

Also you can just get the circuit board with no db9 either. Lots of options to go from ttl to 232. You can also get fully isolated ones as well, handy when plugging into strange db9’s.

isolated ttl to 232

Yeah the ardusimple one is an expensive max232, got lazy and picked those on same order with an extra F9P…