Fix base station + Rover/moving base + heading how to get PVT and ELPOSNED over UART

Q&A forumCategory: QuestionsFix base station + Rover/moving base + heading how to get PVT and ELPOSNED over UART
Marc Stevanin asked 4 weeks ago

I have a LR base/rover kit that is working fine and I am able to get centimeter level position accuracy on my vehicle.
In order to get the heading of the vehicle, I bought an additional simpleRTK2Blite with its antenna and stacked it between the radio module and the simpleRTK2B that was up to now used as a rover for my vehicule. Up to now, I am reading ublox PVT message to get the rover (vehicule) position over simpleRTK2B UART1.
As I understand the setup, by stacking simpleRTK2Blite on simpleRTK2B, simpleRTK2Blite UART1 is automatically connected to simpleRTK2B UART2 and simpleRTK2Blite UART2 is used by the Xbee to get the RTCM data from the fixed base. Then the simpleRTK2Blite board has no more UART interface available. SimpleRTK2B UART1 is still available but if simpleRTK2B board is then used as heading board, how can I get centimeter level accuracy of the of the rover (simpleRTK2Blite) and vehicule heading over the simpleRTK2B UART1 interface?
Thanks in advance for any advice

clive1 replied 4 weeks ago

uBlox doesn’t provide for forwarding/tunnelling data across the ZED devices.
If you want data from both you’ll need to connect to the UARTs, perhaps using the JST connection.

Marc Stevanin replied 4 weeks ago

Thanks for your reply.
Ok, no tunnelling.
But as UART does not allow more than 2 devices on the same bus, how can I retrieve position of the simpleRTK2Blite working as rover/moving base?
Otherwise, as my uC board only has one UART interface left, is there a way to communicate only with the simpleRTK2B heading board getting its absolute position through PVT? What would then be the accuracy?

clive1 replied 4 weeks ago

This is why I stacked two simpleRTK2B (2x F9P, or F9P+F9H) boards, and wired on to a radio subsystem with two UARTs

You can pull PVT and RELPOSNED off the secondary receiver, but this tends to be more fragile, and twice removed from the fixed reference station. I haven’t quantified the accuracy, not my use case, but realistically it is going to be rougher and in Fixed RTK less often.

The F9H will not report position.

I personally think uBlox should have implemented this in a way that the primary receiver could report pitch, roll, yaw with feedback from secondary, and tertiary receiver configurations. And be aware of rigid geometry where applicable. Would likely need a customer with a large carrot or stick.

Marc Stevanin replied 4 weeks ago

It’s look a bit more complicated than I was expecting… I think I will add an arduino Mega that have enough serial interface. The arduino could work as a gateway. It could read the RTCM coming from the fixed base station though the Xbee (i.e. arduino Serial1) and resend it directly to the rover/moving base (i.e arduino Serial2). On the same UART (i.e. arduino Serial2) it will get PVT/RELPOSNED of the rover/moving base. SimpleRTK2B UART1 will comunicate RTCM for heading to simpleRTK2Blite UART2 giving back its heading with RELPOSNED (not sure for this point…). And finally a third arduino serial interface (i.e. Serail3) will send interesting datas to the main uC board of my vehicule.

I am not sure about the concept, simpleRTK2Blite used as rover/moving base will provide RTCM datas to simpleRTK2B heading, how this heading information is retrieved by the rover/moving base? Heading board is reponding to moving base through ublox RelPosNED and then the same RelPosNED infos are available on the moving base device?
Once more thanks for your kind help!

Ardusimple Staff replied 2 weeks ago

Hi Marc,
If you only have one uart left, you can read heading + position from the simpleRTK2B board, but the only disadvantage is that you will have the added error from “static base” to “moving base” + “moving base” to “rover”.