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Comment by cozzyd | Hacker News Reader

Affordable differential GPS would be a nice application... it just requires a fast way of synchronization between two devices (CW in the ISM band would probably work, for example).

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RTK gps is better and quite affordable now. Look it up, you can use two receivers costing maybe $15 each for it.

Do you happen to know a good introduction to how one would use it? I've looked at tools around it a few times, but always didn't find the point where it made "click" on how to actually do anything with them.

Yes! Check out this awesome blog.

https://deepsouthrobotics.com/2017/04/20/spilling-the-beans-...

https://deepsouthrobotics.com/2019/06/03/the-taming-of-the-u...

https://deepsouthrobotics.com/2019/05/23/piecing-together-an...

Thank you!

You set up the base station over a known point, and now your rover unit can give you cm level accuracy when it's within range of the base station (UHF radio range generally).

For a practical application, let's say you wanted to lay out crops for a small hobby farm. This can make getting your base station set up, because you might not care as much about absolute location, which would require finding a surveyed benchmark. Instead you put your base exactly on the corner of your plot, and after setting up a local grid system you can now exactly layout your farm according to your plan. You simply walk around with the rover unit and can get real time cm accurate "coordinates."

Take a look at rtklib.com for software and instructions on https://wiki.openstreetmap.org/wiki/RTKLIB. There are quite a few u-blox receivers that work, also receivers from other brands. If you want to try dual frequency for improved accuracy, u-blox launched an affordable dual frequency chip in 2019.

Surely that little only gets you single-frequency receivers? So you'd be waiting around for 10 minutes to resolve ambiguities every time you got near a tree, bridge or building?

Or can you get multi-frequency receivers for that little these days?

I've just started looking into RTK GPS. My state has a Trimble network that I might use. My application is, weirdly, something a lot like the waypoints of old Garmin GPS handhelds for hikers, only more accurate. I need to be able to lay down a series of points as I drive (perhaps around 30 mph or so) to map out a street network.

However, as I look around trying to find something I can just drop into my car and pull the data from (SD card? USB port?) later on, I haven't seen all of the RTK goodness trickle down yet into something relatively brain-dead and simple to use for my rather small case. I am definitely seeing kits and modules, and some stuff built into high-end drones, but it hasn't seemed to make its way down to my level yet and I am a little curious as to why (or if I am just not looking in the right place for the right thing).

Well, $265 (+antenna $60), but I purchased an Emlid Reach M+ [1] for drone RTK experiments, and it has been pretty simple to use... comes with a really nice UI on the device and internal storage in the unit. Also their website has good documentation, which is helpful since there is a lot to learn about how to do RTK.

Found a local NTRIP caster (within 10 km, lucky I am in range of a public RTK2go one) and the Reach uses the mobile hotspot on my phone to connect to the caster. After a couple seconds to minutes, it settles down to a 10-12 mm accurate fix in lat, lon, alt, and is kinematic so it maintains the accuracy as I am flying the drone around. It records the whole thing internally, or you can have various output modes like standard NMEA over serial, or bluetooth to your phone.

Also, I have used it to record data internally then post-process it for PPK using the county's publically-available RINEX files [2] and Emlid's RTKLIB fork [3].

[1] https://emlid.com/reach/ [2] https://geodesy.noaa.gov/CORS/standard1.shtml [3] https://docs.emlid.com/reach/common/tutorials/gps-post-proce...

Which receivers?

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