Let the receiver pick the base station
Setting up RTK usually means finding a base station yourself, typing in the caster address, the mountpoint and the port, and doing it again whenever you travel. KUON GEO serves 2,485 public base stations worldwide as one open list, so the device can measure the distances itself and connect to the nearest one it is allowed to use. The whole thing is one header file.
The problem: base stations are registered by hand
RTK needs corrections from a base station, and accuracy falls away as the baseline — the distance between you and that station — grows. So the station you should use changes as you move. In practice most people register one station and keep using it, even a hundred kilometres away, because changing it means looking up a new caster and mountpoint by hand.
One open list, no authentication
KUON GEO polls the public casters (RTK2GO, BizStation, GeoRTK, Centipede-RTK) every ten minutes and keeps the roster and liveness of every station. 2,485 stations worldwide as of 2026-08-13 — 417 of them in Japan, 122 in the United States, 90 in Finland, 50 in the United Kingdom, 45 in Canada, 42 in Poland, 29 in Germany. The list is served openly, with no key and no account:
GET https://kuongeo.com/api/bases?jp=1&fmt=tsv&off=0&lim=500
Each row carries position, distribution format, RTCM message types, supported constellations, bitrate, whether authentication is required, whether it costs money, how many times it answered in the last 30 days, and whether it is alive right now. Note that we distribute the roster and liveness only — we do not collect the observation data itself.
The device measures the distance
Give the part your current position and it reads the list one line at a time, computes the great-circle distance on the device, throws away anything outside your range and keeps the nearest ten. 2,485 stations do not exhaust the memory of a small microcontroller, because nothing is held all at once.
Using it is two lines. Take the nearest station and put its host, mountpoint and port where your existing NTRIP settings already live. You do not rewrite the part that connects.
What we measured
At Obihiro, Hokkaido (42.9236, 143.1961) there were 14 stations within 50 km, the nearest at 12.3 km (measured 2026-08-12). The closest four were all open, free and alive: no username, no password. A device that picks for itself would have connected to a station 12 km away instead of whatever was registered months ago.
Things we will not hide
Reject the paid stations and the ones that need a key in your own code. Closing off the path to an unexpected bill is the responsibility of whoever builds the device, so the part hands you those flags rather than deciding for you.
A Fix cannot be promised. It depends on the baseline, the antenna and how much sky you can see. Within 10 km you can expect a fix in tens of seconds; beyond 40 km it often will not come. Show carrSoln (0 = single, 1 = Float, 2 = Fixed) as it is. Never dress a Float up as centimetres — that is the minimum courtesy in this field.
Cost, and why it is free
The list is cached for 120 seconds at the edge, so however many devices ask, the request behind it runs at most once every two minutes. Ten thousand devices asking three times a day is well inside what the platform already includes. There is no meter and no key, and we do not plan to add one — a base station roster is a public good, and so is knowing which stations are alive.