GNSS PPP Product Reference

This document covers naming conventions, file formats, and product types used in Precise Point Positioning (PPP) and PPP with Ambiguity Resolution (PPP-AR).

IGS Long Filename Convention

Most modern products follow the IGS long filename convention:

<AC><TYPE>_<YYYYDDDHHMM>_<LEN>_<SMP>_<CNT>.<FMT>

Field	Description	Example
AC	Analysis Center	IGS, COD, GFZ, WHU
TYPE	Product type	ORB, CLK, ERP, BIA
YYYYDDDHHMM	Start epoch (year + day-of-year + time)	20231230000
LEN	Product length	01D (1 day), 01H
SMP	Sampling interval	05M, 30S
CNT	Content descriptor	ORB, CLK
FMT	File format	SP3, CLK, ERP

Example:

IGS0OPSFIN_20231230000_01D_05M_ORB.SP3

Product Types

Precise Orbit (SP3)

High-accuracy satellite positions replacing broadcast ephemerides.

Convention	Pattern	Example
Legacy	`igsWWWWD.sp3`	`igs22341.sp3`
Modern	`AC0OPSFIN_YYYYDDDHHMM_01D_05M_ORB.SP3`	`IGS0OPSFIN_20231230000_01D_05M_ORB.SP3`

Precise Clock (CLK)

Satellite clock error corrections.

Convention	Pattern	Example
Legacy	`igsWWWWD.clk`	`igs22341.clk`
Modern	`AC0OPSFIN_YYYYDDDHHMM_01D_30S_CLK.CLK`	`IGS0OPSFIN_20231230000_01D_30S_CLK.CLK`

Earth Rotation Parameters (ERP)

Encodes polar motion (x_p, y_p), UT1-UTC, and length-of-day (LOD) for the transformation between the International Terrestrial Reference Frame (ITRF) and the International Celestial Reference Frame (ICRF). Required for orbit integration and precise coordinate transformation in PPP.

Convention	Pattern	Example
Legacy	`igsWWWWD.erp`	`igs22341.erp`
Modern	`AC0OPSFIN_YYYYDDDHHMM_01D_01D_ERP.ERP`	`IGS0OPSFIN_20231230000_01D_01D_ERP.ERP`

Bias Products (BIA)

Three distinct bias types are used in modern GNSS processing:

Type	Abbreviation	Purpose	Required for
Observable-Specific Bias	OSB	Signal-specific hardware delay (multi-GNSS, multi-frequency)	Float PPP, PPP-AR
Fractional Cycle Bias	FCB / phase bias	Fractional part of ambiguity — enables integer fixing	PPP-AR only
Differential Code Bias	DCB	Legacy inter-frequency code delay	Ionosphere modeling (legacy)

OSB supersedes DCB for modern multi-GNSS processing. FCB (or its equivalent under the integer recovery clock / decoupled clock models) is required to fix carrier-phase ambiguities to integers in PPP-AR. Without it, PPP produces a float solution.

Product	Pattern	Example
OSB	`AC0MGXFIN_YYYYDDD0000_01D_01D_OSB.BIA`	`WUM0MGXFIN_20231230000_01D_01D_OSB.BIA`
Phase Bias / FCB	`AC0MGXRAP_YYYYDDD0000_01D_30S_ABS.BIA`	`CAS0MGXRAP_20231230000_01D_30S_ABS.BIA`

Ionosphere Products (IONEX)

Global ionosphere maps providing total electron content models.

Convention	Pattern	Example
Legacy	`igsgDDD0.YYi`	`igsg1230.23i`
Modern	`AC0OPSFIN_YYYYDDD0000_01D_02H_GIM.INX`	`IGS0OPSFIN_20231230000_01D_02H_GIM.INX`

Troposphere Products

Atmospheric delay estimates improving vertical accuracy.

AC0OPSFIN_YYYYDDD0000_01D_05M_TRO.TRO

Antenna Calibration (ANTEX)

Phase center offset (PCO) and phase center variation (PCV) models for both receiver and satellite antennas. Must be consistent with the reference frame (ITRF realization) used for the orbit and clock products.

File	Frame	Status
`igs14.atx`	IGS14/ITRF2014	Superseded — deprecated since IGS Repro3 (late 2022)
`igs20.atx`	IGS20/ITRF2020	Current — required when using IGS Repro3 or later products

Using igs14.atx with Repro3 or post-Repro3 orbit/clock products introduces a frame inconsistency of order 1–2 cm. Always match the ANTEX to the reference frame of the orbit solution.

Reference Frame / SINEX

Weekly SINEX solutions:

Convention	Pattern	Example
Legacy	`igsWWWW.snx`	`igs2234.snx`
Modern	`AC0OPSFIN_YYYYDDD0000_07D_07D_SOL.SNX`	`IGS0OPSFIN_20231230000_07D_07D_SOL.SNX`

Satellite Attitude (OBX)

Satellite attitude quaternions used when processing LEO data or when applying precise antenna orientation corrections beyond the nominal yaw-steering model.

AC0OPSFIN_YYYYDDD0000_01D_05M_ATT.OBX

Note: Real-time SSR streams (NTRIP/RTCM) are not supported by this library.

Observation Data (RINEX)

RINEX 2

ssssDDD0.YYo          (observation)
ssssDDD0.YYd.Z        (compressed)

RINEX 3+

SSSS00CCC_R_YYYYDDDHHMM_01D_30S_MO.rnx.gz

Complete Product Summary

Product Category	Product Name	Purpose in PPP	Format	Sampling	Latency
Observations	GNSS Observation	Raw code and carrier-phase measurements	RINEX OBS	1–30 s	—
Precise Orbits	SP3	Satellite positions in ITRF (replaces broadcast ephemeris)	SP3	5–15 min	ULT ≤3 h / RAP ≤17 h / FIN ≥13 d
Precise Clocks	CLK	Satellite and receiver clock corrections at RMS < 100 ps (FIN)	RINEX CLK	30 s (FIN/RAP) / 5 min (ULT)	ULT ≤3 h / RAP ≤17 h / FIN ≥13 d
Observable-Specific Bias	OSB	Signal-level hardware delays; supersedes DCB for multi-GNSS/multi-freq	SINEX BIAS	Daily	RAP / FIN
Fractional Cycle Bias	FCB / phase bias	Fractional ambiguity terms enabling PPP-AR integer fixing	SINEX BIAS	Daily / 30 s	RAP / FIN
Earth Rotation Parameters	ERP	Polar motion (x_p, y_p), UT1-UTC, LOD for ITRF↔ICRF	ERP	Daily	RAP / FIN
Ionosphere	GIM (IONEX)	Global TEC grid for single-frequency or ionosphere-constrained PPP	IONEX	2 h (FIN) / 15 min (RTS)	RAP / FIN
Troposphere	VMF1/VMF3	Vienna Mapping Function grids (superior to Saastamoinen for high accuracy)	GRID	6 h	FIN
Antenna Calibration	ANTEX	PCO/PCV for receiver and satellite antennas; must match orbit frame (igs20)	ANTEX	Static	FIN
Satellite Attitude	OBX	Attitude quaternions for LEO processing or precise antenna orientation	OBX	5–15 min	RAP / FIN

Typical PPP Processing Directory

ppp_run/
├── obs/
│   └── station.rnx
├── products/
│   ├── orbit.sp3
│   ├── clock.clk
│   ├── erp.erp
│   ├── bias.bia
│   ├── ionosphere.inx
│   ├── antenna.atx
│   └── troposphere.tro
└── output/
    ├── position.pos
    └── residuals.txt