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.
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
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 | 2^nn mm |
| 65-66 | Y Std Dev Exponent | 2^nn mm |
| 68-69 | Z Std Dev Exponent | 2^nn mm |
| 71-73 | Clock Std Dev Exponent | 2^nn 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
#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
Technical References
