Can I get ~1cm accuracy with a 2.5m accuracy GPS module and RTCM/NTRIP data after post processing?

Question

I'm a new on this, so I have a subscription to a RTK? service that sends correction data (RTCM/NTRIP) over GPRS/UMTS (you get a SIM card with the subscription)

I'm also having a Rover of around 2mx1.5m that navigates based on a Python script that runs on a Raspberry (Companion Computer) to which a Pixhawk (controller) is connected to control the whole rover and peripherals. The Pixhawk has a uBlox neo 6m GPS module connected to it (I read somewhere 2.5m accuracy?)

Is it somehow possible to get the correction signal from the SIM card subscription and combine it with the not so accurate GPS module to create a better accuracy signal after post-processing? What I then can inject into the Pixhawk controller? Is this even possible or should I get a RTK GPS module where I can inject the correction data into the GPS module (is this how it works?) (I assume the RTK GPS processes the data and spits out a cm level accurate position?)

I need better accuracy when the rover is driving over agriculture land and I'm already having the expensive RTK subscription so I better use it.

Answer 1

uBlox Neo-6 can use real-time corrections to improve accuracy - technically, it will only use RTCM 2.3 message types 1, 2, 3, 9, which would usually be provided in an NTRIP stream which has a name containing "DGPS" or DGNSS". You can read about the uBlox requirements in the uBlox6 protocol specification. The uBlox u-Center application can be used to supply RTCM corrections to a uBlox receiver, but u-Center only runs on Windows.

A full-accuracy RTK stream is unlikely to contain these messages - professional users of NTRIP corrections usually want decimeter or centimeter accuracy, which requires a different set of messages, nowadays usually in RTCM3 format which Neo-6 will not understand - but NTRIP correction suppliers sometimes provide DGPS or DGNSS corrections for less demanding users.

From my experience with uBlox receivers in Trimble equipment, you could hope to get accuracy of around 1M to 2M but it's very dependent on the antenna which is used.

Note that the quoted accuracy for Neo-6 receiver has lots of conditions "CEP, 50%, 24 hours static, -130dBm, SEP: <3.5m", so don't rely to heavily on manufacturer specifications!

Answer 2

Actually if your are going to work close to any of these RIMS https://egnos-user-support.essp-sas.eu/new_egnos_ops/resources-tools/edas-dgnss-coverage-map you can expect good accuracy values since the uBlox Neo-6 supports SBAS / EGNOS. Click on the area where you will work to see the best accuracy you can get with DGNSS, you can also get better accuracy with SBAS than with GPS in any other areas just by using the EGNOS corrections obtained with your Neo-6. EGNOS is available for free in the EU. In any case you would need to create an EDAS Account to make use of this DGNSS service and configure it in your device, It works for us. The guys from their helpdesk assisted us to create an account and suggested info based on our particular use-case.