GPS-client

A minimal, dependency-free NTRIP rover client for inspecting an RTKBase caster. It connects to a mountpoint, reads the live RTCM3 correction stream, validates each message with CRC-24Q, and prints a rolling dashboard of exactly what a rover needs to obtain an RTK fix.

What it shows

• Base station position decoded from RTCM 1005/1006 (ECEF → lat/lon/height)
• Constellations and satellite counts from the MSM observation messages
• RTK readiness — whether base position + observations are present
• Message inventory — each RTCM type, its rate, and time since last seen
• Throughput and CRC integrity of the stream

Usage

# Local RTKBase caster (defaults: 192.168.1.10:2101, mount RTK-BASE, no auth)
./ntrip_client.py

# Explicit target
./ntrip_client.py --host 192.168.1.10 --port 2101 --mount RTK-BASE

# With basic auth
./ntrip_client.py -u myuser -p mypass

# List the caster's mountpoints and exit
./ntrip_client.py --sourcetable

# Run for a fixed time (headless / logging), refresh every 2s
./ntrip_client.py --duration 30 --interval 2

Rover mode — feed a locally-attached receiver

Pipes the caster's corrections into a second GNSS receiver on a serial port and reads back its live fix quality (Single / DGPS / RTK-Float / RTK-Fixed). Requires pyserial.

# Rover receiver on /dev/ttyACM1 (a SEPARATE receiver from the base)
./ntrip_client.py --rover-port /dev/ttyACM1 --rover-baud 115200

# For a VRS / networked caster that requires a client position upstream:
./ntrip_client.py --rover-port /dev/ttyACM1 --send-gga

The dashboard shows FIX STATUS, position, sats used, HDOP, correction age, and confirms corrections are flowing into the receiver.

Guides

• FRESH-INSTALL.md — build the whole base + rover system from a blank SD card (Raspberry Pi OS → RTKBase → receiver config → rover).
• SETUP-GUIDE.md — reference for the running system: concepts, data-flow diagram, fix-status table, and troubleshooting.

Press Ctrl-C to stop. Requires only Python 3 (standard library).

Example output

NTRIP rover view  ->  192.168.1.10:2101/RTK-BASE
uptime   12.2s   91 msgs   8.4 KiB   5.6 kbit/s   CRC errors: 0
----------------------------------------------------------------
BASE POSITION : 51.47700000, -0.00140000   46.000 m (ellipsoidal)
SATELLITES    : 17 total   GLONASS:8  GPS:9
RTK READINESS : base_pos=Y  observations=Y  ephemeris=N  -> READY for rover RTK
----------------------------------------------------------------
 type   count    rate    age  name
 1005       2    0.2/s   1.9s  Base ARP position (ECEF)
 1077      12    1.0/s   1.0s  GPS MSM7 obs
 1087      12    1.0/s   1.0s  GLONASS MSM7 obs
 ...

Testing

Unit tests cover the pure (non-network) decoding logic in ntrip_client.py. They use only the standard library, so no fixtures or hardware are needed:

python3 -m unittest -v test_ntrip_client.py

test_ntrip_client.py contains 13 tests in four groups:

Group	What it checks
CRC24Q	CRC-24Q validation against a real captured RTCM3 1077 frame (header+payload CRC equals the trailing 3 bytes), detection of a flipped byte, and the empty-input case
Ecef	ecef_to_llh ECEF→lat/lon/height conversion at the equator/prime-meridian and a typical mid-latitude surface point
Nmea	NMEA checksum validation, GGA parsing (RTK-fixed quality, sat count, correction age), S/W sign handling, GST accuracy, and rejection of non-GGA sentences
MsgNames	RTCM message-type → constellation mapping and human-readable names

These run automatically in CI (see the badge above) on Python 3.9–3.13 for every push and pull request, alongside a py_compile check of the client.

Notes

• ephemeris=N is normal and does not block RTK — a rover gets ephemeris from its own receiver. The base only needs to send observations + its position. Ephemeris messages (1019/1020/…) appear intermittently.
• This is a monitor/diagnostic client: it verifies the correction feed. A real positioning rover feeds this same RTCM3 stream into its GNSS receiver (or an RTK engine such as rtkrcv/str2str) alongside its own observations.