Huge delta/deviations in GPS position

WisBlock
1

Please include the following information, in order for us to help you as effectively as possible.

  • What product do you wish to discuss? RAK19007/RAK4631 and WisMesh Pocket

  • What firmware are you using? RUI3

  • What firmware version? 2.5.13

The xmas holidays gave me the chance to dive deep into the Meshtastic world and finally build the “Meshenger” (also one with RAK14000, thanks Bernd!!!), but when I put both my devices out the window, I get quite a discrepancy. Both devices were erase-flashed, then flashed with the same firmware. I left them outside for a couple of hours (Pocket in an upright position) and got this reading (see attached picture). I also noticed, that sometimes, when I wake the Pocket, I get “GPS is disabld”, but after some time, it detects and re-connects to the satellites. On the Messenger (19007/4631) I never had any problems…

gps_delta
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2

I don’t see a big discrepancy, it is ~13m is location and 23m in height.
Depending on how Meshtastic is setting up and handling the GNSS module that could be “normal”. But I can’t say anything about that.

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(1) Are both devices using the same GNSS antenna?
(2) Are both antennas pointing towards the sky?
(3) In your “Messenger”, where is the GNSS antenna, what is around it and how thick is the material of the enclosure wall and what material is the enclosure wall?
(4) What are your settings in the Meshtastic app for these two devices. There are precision options in the channel settings for the the location. But I am not sure if they are influencing what is shown on the display. That is something for Meshtastic to answer.
(5) How many satellites are the devices seeing? (This is on the other page of the display)

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3

Oh… I was checking on the location screen and it showed roughly 1.7km (see picture), so I didn’t check the coordinates, my bad!

  1. I’m not sure about the Pocket’s antenna, but the Meshenger has a RAK12500
  2. The Pocket is standing upright, Meshenger’s antenna shows the hole with adhesive strip up
  3. The Mehenger’s GNSS antenna is on the right side of the OLED next to it (under the black pattern)
  4. Both are in Long-Fast, no channel setup, no configuration yet…
  5. The Meshenger had 6 sats, the Pocket 11

I noticed, that the Pocket was 1 second ahead of http://uhr.ptb.de, the Meshenger half a second behind, but that should be no problem, since the sats send their own time stamp, right?

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4

Less satellites == lower precision
Time is from satellites, I guess the difference is from different acquisition time.

What material is the “black pattern”.
Some plastic with dark/black colors contain materials that are blocking RF signals.

The WisMesh Pocket is using the same GNSS chip and antenna that comes with the RAK12500.

5

The cover consists of very thin PLA, but according to the raw coordinates, everything is fine. Still wondering, where those “1796 m” respectively “1788 m” come from, according to some meshtastic tutorials it should refer to the distance of the shown device, but those number are outright wrong… :smiley:

6

Can’t say anything about how Meshtastic calculates and displays devices locations. This is a question to ask directly to Meshtastic.