SP3 (Standard Product 3)

For the complete documentation index, see llms.txt.

The Standard Product 3 (SP3) format is an ASCII standard developed by the International GNSS Service (IGS) for distributing satellite orbit and clock correction data. Originally designed for GPS satellites, SP3-c (the current version) supports multiple GNSS constellations and LEO satellites, making it widely used for precise orbit ephemerides.

VALAR Measurement Import Requirements

SP3 permits position-only products and optional accuracy/correlation records. VALAR’s current OD measurement importer is narrower: it accepts PV observations, not position-only observations.

Supply a velocity-capable (V) header and matching P and V records for the same satellite at each epoch. Missing velocity is an error, not zero velocity. Do not change the header alone or insert zero V records unless those are actual supplied observations; genuine zero velocity is preserved.
Supply positive finite accuracy for all three position and all three velocity components in the P/V records. When PVT measurement uncertainty is enabled, only missing components use the shared spacecraft defaults or per-import override; supplied accuracy is preserved. Otherwise missing or partial accuracy produces “SP3 measurement uncertainty is required”. Header aggregate orbit accuracy is not a six-component noise model.
Supply a supported coordinate system in the header; a missing frame is not assumed to be ITRF.
EP/EV accuracy and correlation records are currently rejected because the underlying parser would discard them. Ask the producer for an OEM containing PV states and covariance at every epoch to preserve that uncertainty.

For a position-only or matching satellite P record error, obtain genuine paired PV data with uncertainty or use a consumer that supports position-only products. This restriction does not make a P-only SP3 product invalid under the SP3 standard.

Key Components

An SP3 file contains several distinct sections:

Header: 22 lines of file-level metadata including version, time system, coordinate frame, satellite list, and accuracy information
Comments: 4 optional comment lines for additional documentation
Epoch Blocks: Repeating blocks containing position/clock records and optional velocity/correlation records
EOF Marker: End-of-file indicator

File Structure Overview

Header Lines (1-22)
├── Line 1: Version, start time, epochs, coordinate system, orbit type
├── Line 2: GPS week, seconds of week, epoch interval, MJD
├── Lines 3-7: Satellite identifiers (up to 85 satellites)
├── Lines 8-12: Orbit accuracy exponents
├── Line 13: File type and time system
├── Lines 15-16: Standard deviation base values
└── Lines 19-22: Comments

Data Section
├── Epoch Header (* YYYY MM DD HH MM SS.ssssssss)
├── Position Records (P)
├── Position Correlation Records (EP) [optional]
├── Velocity Records (V) [optional]
└── Velocity Correlation Records (EV) [optional]

EOF

Header Fields

Line 1: File Identification

Columns	Field	Description
1-2	Version	`#c` for SP3-c format
3	P/V Flag	`P` = position only, `V` = position and velocity
4-31	Start Time	Year, month, day, hour, minute, second
33-39	Epochs	Number of epochs in file
41-45	Data Used	Measurement type descriptor (e.g., `ORBIT`)
47-51	Coordinate System	Reference frame (e.g., `ITR14`, `IGS14`)
53-55	Orbit Type	`FIT`, `EXT`, `BCT`, or `HLM`
57-60	Agency	Producing agency identifier

Line 2: Time Reference

Columns	Field	Description
4-7	GPS Week	GPS week number
9-23	Seconds of Week	0.0 to 604800.0
25-38	Epoch Interval	Time between epochs (seconds)
40-44	MJD	Modified Julian Day at start
46-60	Fractional Day	Decimal fraction of day

Lines 3-7: Satellite Identifiers

Up to 85 satellites listed across 5 lines (17 per line). Each satellite uses a system identifier:

Letter	System
G	GPS
R	GLONASS
E	Galileo
C	BeiDou/COMPASS
J	QZSS
L	LEO satellites

Line 13: File Type and Time System

Columns	Field	Values
4-5	File Type	`G` (GPS), `R` (GLONASS), `M` (mixed), `L` (LEO), `E` (Galileo), `C` (COMPASS), `J` (QZSS)
10-12	Time System	`GPS`, `GLO`, `GAL`, `TAI`, `UTC`, `QZS`

Data Records

Position and Clock Record (P)

P G01  15000.123456  -5000.654321  20000.987654    123.456789  1  2  3  10

Columns	Field	Units
1	Record Type	`P`
2-4	Satellite ID	System letter + PRN
5-18	X Position	kilometers
19-32	Y Position	kilometers
33-46	Z Position	kilometers
47-60	Clock Correction	microseconds
62-63	X Std Dev Exponent	position/velocity base from `%f`, raised to nn, in mm
65-66	Y Std Dev Exponent	position/velocity base from `%f`, raised to nn, in mm
68-69	Z Std Dev Exponent	position/velocity base from `%f`, raised to nn, in mm
71-73	Clock Std Dev Exponent	clock base from `%f`, raised to nn, in ps

Bad or absent position values are set to 0.000000. Bad or absent clock values are set to 999999.999999.

Optional Flags (Position Record)

Column	Flag	Meaning
75	Clock Event	`E` = discontinuity, blank = normal
76	Clock Prediction	`P` = predicted, blank = observed
79	Maneuver	`M` = orbit maneuver, blank = normal
80	Orbit Prediction	`P` = predicted, blank = observed

Velocity and Clock Rate Record (V)

Only present when Line 1 P/V flag is V:

Columns	Field	Units
1	Record Type	`V`
2-4	Satellite ID	System letter + PRN
5-18	X Velocity	decimeters/second
19-32	Y Velocity	decimeters/second
33-46	Z Velocity	decimeters/second
47-60	Clock Rate	10^-4 microseconds/second

Correlation Records (EP, EV)

Optional high-precision correlation records provide:

Standard deviations in physical units (mm for position, mm/s for velocity)
Six correlation coefficients (xy, xz, xc, yz, yc, zc) scaled by 10^7

Supported Time Systems

Code	Time System
GPS	GPS Time
GLO	GLONASS UTC
GAL	Galileo System Time
TAI	International Atomic Time
UTC	Coordinated Universal Time
QZS	QZSS Time

All times in an SP3 file use the SAME time system, whether expressed as Gregorian dates or Modified Julian Dates.

Common Use Cases

Precise Point Positioning (PPP): High-accuracy GNSS positioning using precise orbits
Orbit Comparison: Validating orbit determination results against IGS products
LEO Satellite Tracking: Distributing precise orbits for Earth observation satellites
Clock Analysis: Satellite clock characterization and time transfer
Geodetic Research: Reference frame determination and geophysical studies

Sample SP3-c File

This abbreviated position-only example illustrates the SP3 layout. It is not accepted by VALAR’s PV measurement importer; use the PV and uncertainty requirements above for an importable product.

#cP2024 12 15  0  0  0.00000000      96 ORBIT IGS14 FIT  IGS
## 2341 518400.00000000   900.00000000 60658 0.0000000000000
+   32   G01G02G03G04G05G06G07G08G09G10G11G12G13G14G15G16G17
+        G18G19G20G21G22G23G24G25G26G27G28G29G30G31G32  0  0
+          0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0
+          0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0
+          0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0
++         2  2  2  2  2  2  2  2  2  2  2  2  2  2  2  2  2
++         2  2  2  2  2  2  2  2  2  2  2  2  2  2  2  0  0
++         0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0
++         0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0
++         0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0  0
%c G  cc GPS ccc cccc cccc cccc cccc ccccc ccccc ccccc ccccc
%c cc cc ccc ccc cccc cccc cccc cccc ccccc ccccc ccccc ccccc
%f  1.2500000  1.025000000  0.00000000000  0.000000000000000
%f  0.0000000  0.000000000  0.00000000000  0.000000000000000
%i    0    0    0    0      0      0      0      0         0
%i    0    0    0    0      0      0      0      0         0
/* IGS FINAL ORBIT COMBINATION FROM WEIGHTED AVERAGE OF:
/* cod emr esa gfz grg jpl mit ngs sio
/* REFERENCED TO IGS TIME (IGST) AND target/IGS14
/* CLK ANT Z-OFFSET (M): II/IIA 1.023; IIR 0.000
*  2024 12 15  0  0  0.00000000
PG01  15234.123456  -8234.654321  19876.987654    123.456789
PG02  12456.789012   5678.901234  22345.678901    -45.678901
PG03  -8765.432109  18765.432109  14567.890123    234.567890
EOF

Core Concepts

File Formats

VALAR Measurement Import Requirements

Key Components

File Structure Overview

Header Fields

Line 1: File Identification

Line 2: Time Reference

Lines 3-7: Satellite Identifiers

Line 13: File Type and Time System

Data Records

Position and Clock Record (P)

Optional Flags (Position Record)

Velocity and Clock Rate Record (V)

Correlation Records (EP, EV)

Supported Time Systems

Common Use Cases

Sample SP3-c File

Technical References

​VALAR Measurement Import Requirements

​Key Components

​File Structure Overview

​Header Fields

​Line 1: File Identification

​Line 2: Time Reference

​Lines 3-7: Satellite Identifiers

​Line 13: File Type and Time System

​Data Records

​Position and Clock Record (P)

​Optional Flags (Position Record)

​Velocity and Clock Rate Record (V)

​Correlation Records (EP, EV)

​Supported Time Systems

​Common Use Cases

​Sample SP3-c File

​Technical References

VALAR Measurement Import Requirements

Key Components

File Structure Overview

Header Fields

Line 1: File Identification

Line 2: Time Reference

Lines 3-7: Satellite Identifiers

Line 13: File Type and Time System

Data Records

Position and Clock Record (P)

Optional Flags (Position Record)

Velocity and Clock Rate Record (V)

Correlation Records (EP, EV)

Supported Time Systems

Common Use Cases

Sample SP3-c File

Technical References