[OSM-talk] Affordable 1 CM high precision GPS.

[Greg Troxel]

John Whelan <jwhelan0112 at gmail.com> writes:

> Search Youtube for "Andreas Spiess ESP32 precision GPS receiver
> (incl. RTK-GPS Tutorial)"  I deliberately haven't put a direct link
> in.
>
> It needs packaging and documenting but I think this sort of
> differential GPS could be very useful in accurate mapping.

comments without watching :-)

  RTK can be done for not a huge amount of money, less than a moderate
  phone and a lot less than a new high-end phone.  The u-blox F9P is
  about $200.  A decent antenna is another $100.  You need power and
  cabling of course.  You then need to get RTK reference data and inject
  it, and the F9P will compute RTK solutions.  I have an F9P; with good
  reference data and a decent antenna, it works very well with clear sky
  and ok in the forest, getting you fairly reliably within about a 1 m
  vs 10 m non-RTK.

  If you don't have a local RTK network reference you can run your own,
  with double the hardware and some work to find the location of your
  fixed antenna.

  1 cm is a bogus claim; I have returned to the same piece of rebar
  multiple times and the 30-sec averages cluster in a diameter of about
  4 cm.  I do not know if there is systematic offset.  People tend to
  believe the accuracy numbers they get out of the device and believing
  them does not make sense.

  One can also use rtklib with a receiver that outputs raw, without
  needing an F9P.  This is less expensive and a lot harder.

  This item it out of stock, and a fairly big markup, but
    - it works  (I have a report from a reliable nerd who has mapped
      with it!)
    - it has a battery, a case, a display, a uSD for logging
    - it has an ESP32 to manage the F9P
    - sparkfun has been GREAT about actually working on the firmware
  https://www.sparkfun.com/products/18442
  https://github.com/sparkfun/SparkFun_RTK_Firmware/

  cm accuracy is not really useful for mapping vs 5 cm or 10 cm, but
  having 10 cm accuracy means you can just take the data as accurate.
  trails that you thought you mapped well turn out not to be where the
  map says.  mapping done with RTK is so much neater and cleaner.  It's
  reasonable to map individual rocks and then the map looks like the
  ground and lines up with the imagery.  If you haven't tried it you
  don't know what you are missing.   I don't like to map trails with
  regular GPS any more.