Centimetre level accuracy of RTK board with an antenna

GPS/GNSS
1

We are using “SparkFun GPS-RTK-SMA Breakout - ZED-F9P (Qwiic)” with “u-blox Multi-band Active GNSS Antenna - L1, L5 (ANN-MB5)” with a valid closet GNSS station, my test method is to put the kit on a outdoor chair, first reading is around 8 - 10 metres on the map away from the actual position. When I move the kit one, two, three metres closer, the GPS reading also slightly moves, but still can’t get a centimetre level accuracy. Any idea I can improve it? Thank you

2

Is it getting an RTK fix?
Is the receiver an L1/L2 model or the L1/L5 one?
What map? Are you talking about registration with Google imagery or position relative to an accurately established location for the chair?

3

Hey,

Thank you for the prompt reply.
We use the following Typescript to read message from the Rapsberry PI USB port which links to the RTK board connected with an antenna

import { SerialPort, ReadlineParser } from ‘serialport’;

import * as nmea from ‘nmea-simple’;

const port = new SerialPort({ path: /dev/${process.env?.GPS_USB_PORT}, baudRate: 9600 });

const parser = port.pipe(new ReadlineParser({ delimiter: ‘\r\n’ }));

const packet = nmea.parseNmeaSentence(line);

const { time, latitude, longitude, altitudeMeters, fixType } = packet;

So for your questions:

  1. Not all devices although they share the same configuration and code, some of them displays fixType: fix, some says: fixType: frtk, and sometimes says fixType: delta or fixType: rtk, even the same device, this fixType sometimes changes
  2. We are using u-blox Multi-band Active GNSS Antenna - L1, L5 (ANN-MB5), which is a L1/L5, is L1/L2 better?
  3. The public google map: Google Maps

Thank you again for your reply

4

Seems like the wrong antenna for the receiver.
For cm level positioning, you need an “RTK Fixed” fix type. Does your RTCM3 data source provide L5 observations? L1/L2 infrastructure is more prevalent, and your receiver is likely the L1/L2 model.
Depending on imagery alignment/registration is not advisable. An 8m offset seems a bit high, within the USA I’d expect numbers closer to a metres, but depends a lot on optical distortion and corrections to the underlying imagery.

5

Okay, do you have a proper antenna link to help us achieve the accuracy?
Also I am not quiet sure whether the GNSS stations(is this what you refer to RTCM3 data source?) https://portal.ga.gov.au/persona/pa in Sydney can provide L5 observations or not, if they can only provide L1/L2, does this mean it’s lower accuracy? Thank you

6

For the ZED-F9P-00B series (L1 / L2), look at the ANN-MB-00 or ANN-MB2

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7

Thank you for the advice, I guess this GNSS L1/L2 Multi-Band Magnetic Mount Antenna - 5m (SMA) is the same(ANN-MB-00)?

8

Yep, same :slight_smile:

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