Quick Start: IGS-RTS PPP¶

Conventional float PPP from the IGS Real-Time Service (RTS) — a global, open, real-time RTCM-SSR / IGS-SSR (MT4076) correction stream (orbit, clock, code bias). No base station and no regional augmentation are required; corrections arrive over the internet via NTRIP.

Set correction = "igs-rts" and feed an RTCM-SSR stream alongside your rover observations and a broadcast navigation source. Typical accuracy is ~0.2 m horizontal (float) after convergence — see Expected accuracy.

Prerequisites¶

1. An NTRIP account for an RTS caster. This guide uses NASA CDDIS, which requires a free Earthdata login.
   • Register: https://urs.earthdata.nasa.gov/
   • CDDIS real-time / NTRIP overview: Earthdata — GNSS real-time data
   • CDDIS caster stream table (mountpoints): CDDIS — Data caster streams
2. stunnel — CDDIS serves NTRIP over TLS (port 443). MRTKLIB has no built-in TLS stack; tunnel through stunnel. See NTRIP Streams → TLS for the full setup. The minimal tunnel config is shown below.
3. A dual-frequency rover. Geodetic receivers (GPS L1/L2, GAL E1/E5a) are ideal. Other RTS casters (BKG products.igs-ip.net, etc.) work the same way.

Streams and mountpoints¶

An IGS-RTS PPP run needs three data sources. On CDDIS:

Notes:

• SSR provider variants. SSRAxxIGS0 is the IGS combined product in the global ITRF frame; provider-specific streams exist too (SSRA00CNE0 CNES, SSRA00WHU0 WHU, …). Prefer the ITRF variant — the _SIRGAS2000 variants are re-projected for South America and add a frame bias elsewhere. CNES streams additionally carry phase bias (future PPP-AR); IGS combined is code-bias only (float).
• SSRA = antenna-phase-center (APC) referenced → use satellite_ephemeris = "brdc+ssrapc". SSRC = center-of-mass → brdc+ssrcom.
• Broadcast ephemeris is required — SSR corrects the broadcast orbit/clock, it does not replace it. Many receiver streams already embed RTCM nav (1019…); if yours does not, add a BCEP* stream (or a RINEX nav file for mrtk post).
• Pick mountpoints from the CDDIS stream table.

Connect (stunnel TLS tunnel)¶

ntrip-tls.conf:

[ntrip-tls]
client = yes
accept = 127.0.0.1:2101
connect = caster.cddis.eosdis.nasa.gov:443

stunnel ntrip-tls.conf      # listens on 127.0.0.1:2101, forwards to CDDIS over TLS

Then connect MRTKLIB through the local endpoint with NTRIP v2 and the &host= header (required by most TLS casters). URL-encode special characters in the password (@ → %40). Full details in NTRIP Streams.

Configuration¶

Sample: conf/igs/rnx2rtkp_igsrts.toml.

[positioning]
mode = "ppp-static"                  # or ppp-kine for a moving rover
frequency = "l1+2"
satellite_ephemeris = "brdc+ssrapc"  # SSRA = APC; use brdc+ssrcom for SSRC
systems = ["GPS", "Galileo"]
correction = "igs-rts"               # must be set explicitly (see note)

[positioning.corrections]
satellite_antenna = false            # SSR_APC orbits are antenna-phase-center based
receiver_antenna = true

[positioning.atmosphere]
ionosphere = "dual-freq"             # iono-free combination
troposphere = "est-ztdgrad"

Running¶

Post-processing (mrtk post)¶

Record the streams to RTCM-3 logs, then process. Capture with mrtk relay (stagger the starts a few seconds apart to avoid simultaneous-connect rejections on CDDIS):

Q='ver=2&host=caster.cddis.eosdis.nasa.gov'
mrtk relay -in "ntrip://USER:PW@127.0.0.1:2101/SSRA02IGS0?$Q"  -out ssr.rtcm3  &
mrtk relay -in "ntrip://USER:PW@127.0.0.1:2101/BCEP00BKG0?$Q"  -out brdc.rtcm3 &
mrtk relay -in "ntrip://USER:PW@127.0.0.1:2101/AIRA00JPN?$Q"   -out rover.rtcm3 &

Convert obs/nav to RINEX, then run PPP (the SSR .rtcm3 log is auto-detected by its extension):

mrtk convert -r rtcm3 -o rover.obs -tr 2026/05/22 14:00:00 rover.rtcm3
mrtk convert -r rtcm3 -n brdc.nav  -tr 2026/05/22 14:00:00 brdc.rtcm3
mrtk post -k conf/igs/rnx2rtkp_igsrts.toml rover.obs brdc.nav ssr.rtcm3 -o out.pos

Real-time (mrtk run)¶

Use the real-time sample conf/igs/rtkrcv_igsrts.toml: it points [streams.input.rover] and [streams.input.correction] at NTRIP mountpoints (type ntripcli) through the stunnel endpoint, with the same [positioning] block as above. Replace USER:PW and the rover stream with your own receiver, then start:

mrtk run -o conf/igs/rtkrcv_igsrts.toml -p 2401 -s

The correction-application pipeline (decode_ssr* → satpos_ssr → corr_meas) is identical to the post-processing path; both reach the same accuracy level.

Expected accuracy¶

Validated on a real CDDIS RTS stream — IGS station AIRA00JPN (GPS L1/L2 + GAL E1/E5a iono-free, TRM59800.00 SCIS), IGS combined RTCM-SSR (SSRA02IGS0) + broadcast ephemeris, against the IGS final SINEX coordinate:

This is conventional float PPP (code-bias-only product). The result agrees with upstream RTKLIB 2.4.3 rnx2rtkp on identical inputs. Integer PPP-AR (a phase-bias product such as CNES CLK9x) is a future addition.

Troubleshooting¶

• correction source not implemented / invalid correction — set satellite_ephemeris = "brdc+ssrapc" (or "brdc+ssrcom"); igs-rts requires it.
• HTTP 401 / no data on capture — check the Earthdata credentials and the &host= header; when capturing several streams at once, start them a few seconds apart (CDDIS rejects bursts of simultaneous connects).
• No solution (Q=0) / metre-level bias — confirm the broadcast ephemeris covers the obs window and that the SSR is the ITRF (not _SIRGAS2000) variant. A real-time MSM RINEX often carries no antenna name; set [antenna.rover] type explicitly so the receiver PCV is applied.
• mrtk run: console open error dev= — pass a telnet port (-p 2401); the follow-on Error: vt is NULL is harmless (no attached terminal).

Next steps¶

• NTRIP Streams — NTRIP versions, TLS/stunnel, password escaping.
• Configuration (TOML) and Config Options Reference.
• Positioning Configuration Model — the correction axis and validity matrix.