NTRIP & RTKLIB Knowledge Patch Skill

NTRIP & RTKLIB Knowledge Patch

Covers NTRIP protocol internals and RTKLIB configuration details that are easy to get wrong: stream path formats differ between tools, parameter names are non-obvious, and NTRIP v1 quirks break standard HTTP libraries.

Reference Files

| File | Contents | |------|----------| | ntrip-protocol.md | NTRIP v1/v2 wire format, GGA requirement for VRS, RTK2go connection details | | rtkrcv-config.md | Full rtkrcv.conf parameters, demo5-specific tuning for u-blox receivers | | str2str-usage.md | str2str relay examples, building demo5 on Linux |

Stream Path Syntax

Stream URLs differ between str2str CLI and rtkrcv.conf — getting these wrong silently fails.

str2str CLI (-in/-out flags):

ntrip://[user[:passwd]@]addr[:port][/mntpnt]
ntrips://[:passwd@]addr[:port][/mntpnt[:str]]
serial://port[:brate[:bsize[:parity[:stopb[:fctr]]]]]
tcpsvr://:port
tcpcli://addr[:port]
file://path[::T][::+start][::xspeed][::S=swap]

rtkrcv.conf path format (no URI scheme — type set separately):

ntripcli : user:passwd@addr:port/mntpnt
ntripsvr : [passwd@]addr:port/mntpnt[:str]
ntripcas : user:passwd@:[port]/mpoint[:srctbl]
tcpsvr   : :port
tcpcli   : addr:port
serial   : port[:bit_rate[:byte[:parity(n|o|e)[:stopb[:fctr]]]]]
file     : path[::T[::+offset][::xspeed]]

See references/rtkrcv-config.md for full rtkrcv.conf parameter reference.

rtkrcv.conf Quick Reference

Key parameter names for stream setup (easy to guess wrong):

# Input streams (1=rover, 2=base, 3=corrections)
inpstr1-type       = serial        # serial|tcpcli|tcpsvr|ntripcli|file|off
inpstr1-path       = /dev/ttyACM0:115200:8:n:1:off
inpstr1-format     = ubx           # ubx|rtcm3|rtcm2|nov|oem3|...
inpstr2-type       = ntripcli
inpstr2-path       = user:passwd@caster.example.com:2101/MOUNTPT
inpstr2-format     = rtcm3

# Output streams
outstr1-type       = file
outstr1-path       = /tmp/solution_%Y%m%d%h%M.pos
outstr1-format     = llh           # llh|xyz|enu|nmea|...

# Log streams (raw data logging)
logstr1-type       = file
logstr1-path       = /tmp/rover_%Y%m%d%h%M.ubx

RTCM MSM Message Numbering

MSM types 1–7 repeat per constellation in blocks of 10:

| Constellation | Range | |---------------|-------| | GPS | 1071–1077 | | GLONASS | 1081–1087 | | Galileo | 1091–1097 | | SBAS | 1101–1107 | | QZSS | 1111–1117 | | BeiDou | 1121–1127 |

MSM4 = pseudorange + phase + CNR (no Doppler). MSM7 = full resolution + Doppler. MSM7 is preferred (1077, 1087, 1097, 1127). Legacy: 1004 (GPS L1+L2), 1012 (GLONASS L1+L2).

See references/str2str-usage.md for -msg flag examples.

NTRIP v1 Wire Protocol (Quick Reference)

RTKLIB only supports NTRIP v1. Key detail for custom client implementations.

Client request:

GET /mountPt HTTP/1.0\r\n
User-Agent: NTRIP theSoftware/theRevision\r\n
Authorization: Basic dXNlcjpwYXNzd29yZA==\r\n
\r\n

Responses:

ICY 200 OK\r\n         # success — binary RTCM follows
SOURCETABLE 200 OK\r\n  # sourcetable (also returned on error)

Note: Some HTTP libraries reject ICY 200 OK as non-standard — must handle explicitly.

See references/ntrip-protocol.md for v2 differences, GGA/VRS requirements, RTK2go setup.

RTK2go Quick Reference

Free public caster at rtk2go.com:2101 (v1+v2) or :2102 (TLS, v2 only).

| Role | User | Password | Notes | |------|------|----------|-------| | Client (rover) | your email | none | Select mountpoint from sourcetable | | Server (base) | — | assigned | Requires reservation at rtk2go.com |

RTKLIB limitation: can only connect as server with Rev1 — do not request Rev2 reservations for RTKLIB-based stations.

Server Parameters

svrcycle           = 10            # processing cycle (ms)
timeout            = 10000         # stream timeout (ms)
reconnect          = 10000         # reconnect interval (ms)
nmeacycle          = 5000          # NMEA GGA send cycle (ms) for VRS
buffsize           = 32768         # input buffer size (bytes)

See references/rtkrcv-config.md for demo5-specific parameters.

str2str Relay (Common Pattern)

# Serial receiver → NTRIP server (base station)
str2str -in serial://ttyACM0:115200#ubx \
        -out ntrips://:password@rtk2go.com:2101/MY_MOUNT#rtcm3 \
        -msg 1077(1),1087(1),1097(1),1127(1),1005(10),1033(10) \
        -p 60.1234 24.5678 45.0

# NTRIP client → file (log corrections)
str2str -in ntrip://user:pass@caster.example.com:2101/MOUNT \
        -out file:///tmp/rtcm_%Y%m%d%h%M.rtcm3

The -msg flag specifies RTCM output messages and intervals in seconds. The -p flag sets station position for 1005/1006 messages.

See references/str2str-usage.md for full path syntax and build instructions.

Demo5 Key Parameters (u-blox Receivers)

Build from rtklibexplorer/RTKLIB, not tomojitakasu/RTKLIB.

# Pseudorange/carrier ratio — 300 for u-blox (default 100)
stats-eratio1      = 300
stats-eratio2      = 300

# Fix-and-hold tracking gain (higher = lower gain, avoids false holds)
pos2-varholdamb    = 0.1           # default 0.001; 0.1-1.0 recommended

# AR filter — delay new/cycle-slip sats if they degrade AR ratio
pos2-arfilter      = on

# Position variance threshold before enabling AR
pos2-arthres1      = 0.004         # 0.004-0.10 typical

# Consecutive fix samples before hold
pos2-arminfix      = 20            # 5-20× sample rate

# Min satellites for fix/hold/drop
pos2-minfixsats    = 4
pos2-minholdsats   = 5
pos2-mindropsats   = 10

See references/rtkrcv-config.md for GLONASS AR and full parameter reference.

GGA Requirement for VRS

VRS/NEAR mountpoints require NMEA GGA sentences periodically so the caster generates position-specific corrections. In rtkrcv.conf:

nmeacycle          = 5000          # GGA send interval (ms)
ant2-postype       = single        # approximate position source

Without GGA, VRS streams may send no data or stale corrections.

Building Demo5 on Linux

git clone https://github.com/rtklibexplorer/RTKLIB.git
cd RTKLIB/app/rtkrcv/gcc && make    # single CUI app
# or: cd RTKLIB/app && make          # all CUI apps

Agent Skills: NTRIP & RTKLIB Knowledge Patch

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