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Re: [Paparazzi-devel] GPS RTK

From: Chris Gough
Subject: Re: [Paparazzi-devel] GPS RTK
Date: Wed, 2 Oct 2013 19:41:08 +1000

Progress towards DGPS with uBlox modules is going OK. Using raw output from e.g. neo6t  module as the fixed groundstation, generating RCTM 2 and sending it to various NEO and LEA rovers.

Current status is that it works quite well most of the time, but there is at least one serious bug (occasional episodes of very poor performance). There hasn't been a commit for a while but it's still being worked on. One theory is that bug is in the uBlox firmware side (RCTM 2 handling code).

Performance of RCTM 2 augmented GPS is approximately equal to SBAS at it's best, carrier-phase corrected but not comparable to RTK or heavily post-processed statistical techniques used by surveyors.  We don't get SBAS in Australia yet, so it's a big improvement for us. (although it may be available soon, when the next Japanese satellite is launched).

The piksi looks really cool (we are backing it) but I think it's a long way from providing a usable RTK solution. The problem with implementing your own RTK is that you would have to reproduce a large proportion the gps firmware stack, which presumably has a lot of heuristic tricks that make it work better. My guess is "the last 10%" will be really hard, but I'd be happy to be wrong about that.

Sending RCTM 2 over telemetry (telecommand) should be quite practical, it's not very high bandwidth. It's precision is limited by message length not bandwidth.

Chris Gough

On 02/10/2013, at 6:27 PM, "Prof. Dr.-Ing. Heinrich Warmers" <address@hidden> wrote:

Hi Piotr,
it would be nice if we can integrate the message uplink for RTK. By using  the navilog 407TTL (13 Euro + 20 Euro for USB-TTL UART interface) it is possible to  have a low cost D-GPS.  If the laptop has to less computer power it is possible to use the raspberry Pi or the beagle.
I think that the paparazzi uplink has enough bandwidth to send every second the uplink for D-GPS.
In 2009 we made experiments with the RTK and the old sam LS module. It woks within 1m tolerance.
It would also be nice if we can use multi-norm receivers like the  NV08C-CSM for paparazzi. This module cost about 40 Euro  and can today  receive GPS and GLONASS .  My smart phone has the same chip set an receive usually 12 to 17 satellites. This module gives the chance to fly multicopters in  towns  and normal wing in small valley.  it can also by used for the D-GPS basis station with RTKlib.
It would by nice if you can make a small PCB for this module with a USB option.


Piotr Esden-Tempski schrieb:
Heinrich, did you read his email at all?! He wants to use the Piksi not Navilog...

afishindouban: I will be adding support for Piksi to paparazzi as soon as the protocol is stable enough that it makes sense. I am in contact with the makers of Piksi and will be adding the necessary drivers.

Piksi comes with it's own radio so it will be exchanging the necessary data for RTK itself. There is no immediate need to integrate the RTK data channel into the telemetry of Paparazzi. But we may do that eventually, to save on amount of radios on the vehicles.


On Oct 1, 2013, at 4:55 AM, "Prof. Dr.-Ing. Heinrich Warmers" <address@hidden> wrote:

the UAV is the rover. On the ground station you have to implement  RTK. You  can do this with the navilog 407TTL or the ublox sam or t modules. This modules can send pseudo ranges.  You have to write messages  from the ground station to the GPS in the UAV.   The result is that the error in the rover is in the 30cm range.
To get a fix for the ground station you need up to 20 minutes.


afishindouban schrieb:
I was think to to use this GPS in the UAV with paparazzi. some one can sometime on spend this ? GPS connetion has no problem, just need to see how to integrate data link of the Autopilot instead of the GPS data link.,with GCS as a RTK base station.
Some one can give idea ? 


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