SP3

SP3 Precise GNSS Orbit file parsing, analysis & production.

This file format is specifid by the International GNSS Service (IGS).

NB: this library only supports revisions C & D (latest).

SP3 files content

SP3 files provide satellite position vector with a high precision (+/- 1mm), which is compatible with high precision geodesy.

Sometimes SP3 files may provide velocity vectors, satellite clock offsets or satellite clock drifts as well.

Getting started

[dependencies]
sp3 = "1"

Parse an SP3 file

use sp3::prelude::*;
use std::path::PathBuf;
use std::str::FromStr;
    
let path = PathBuf::new()
    .join(env!("CARGO_MANIFEST_DIR"))
    .join("data/SP3")
    .join("C")
    .join("ESA0OPSRAP_20232390000_01D_15M_ORB.SP3.gz");

let sp3 = SP3::from_gzip_file(&path).unwrap();

assert_eq!(sp3.header.version, Version::C);
assert_eq!(sp3.header.data_type, DataType::Position);

assert_eq!(
    sp3.first_epoch(),
    Epoch::from_str("2023-08-27T00:00:00 GPST").unwrap()
);

assert_eq!(sp3.total_epochs(), 96);
assert_eq!(sp3.header.agency, "ESOC");

// All coordinates expressed in the following system
assert_eq!(sp3.header.coord_system, "ITRF2");

// Orbit type used in fitting process
assert_eq!(sp3.header.orbit_type, OrbitType::BHN);

// This means all temporal information is expressed in this [TimeScale]
assert_eq!(sp3.header.timescale, TimeScale::GPST);

// This means several constellations are to be found
assert_eq!(sp3.header.constellation, Constellation::Mixed);

// Week counter, in given [TimeScale]
assert_eq!(sp3.header.week_counter, 2277);
assert_eq!(sp3.header.week_sow, 0.0_f64);

assert_eq!(sp3.header.epoch_interval, Duration::from_seconds(900.0_f64));

// Data exploitation
for (epoch, sv, (x_km_ecef, y_km_ecef, z_km_ecef)) in sp3.satellites_position_km_iter() {

}

// Data exploitation
for (epoch, sv, clock) in sp3.satellites_clock_offset_sec_iter() {

}

Lib features

This library comes with a few features

• flate2 will enable direct support of Gzip compressed SP3 files
• serde will unlock internal structure serdes ops
• anise feature will unlock Elevation and Azimuth attitudes (heaviest dependency).
• qc option will unlock basic file management options like Merge(A, B) or Split (timewise)
• processing relies on qc and unlocks file preprocessing, like resampling and data masking
• interpolation methods are proposed by default (they do not involve other dependencies)

Default features

This library is shipped with flate2 support (gzip compressed SP3 files) by default.

Main dependencies

This library relies on Nyx-Space/Hifitime at all times.

The Nyx-Space/ANISE feature is the heaviest library option.

Satellite attitude interpolation

Satellite (SV) attitude interpolation is a major topic in SP3 processing. Because quite often, you will have to match data provided by SP3 (high precision) other datasets, oftentimes expressed in different timescales and most often sampled at higher rate.

Indeed, SP3 is published by laboratories with a typical fit rate of 15'.

To answer the requirement of SP3 processing inside a broader geodetic processing pipeline, this library proposes a few sets of method

• [SP3.satellite_position_interp()] will design the interpolation kernel to which you can apply your custom interpolation function

• [SP3.satellite_lagrangian_position_interp()] will apply the Lagrangian interpolatation method, typically used in geodetic processing piplines, at the desired interpolation order.

• [SP3.satellite_lagrangian_position_interp_x11()] applies the Lagrangian interpolation method with a order of 11, which is typically used to preserve SP3 precision

• [SP3.satellite_lagrangian_position_interp_x17()] applies the Lagrangian interpolation method with a order of 17, which is way more than enough and should be used in processing pipelines where processing speed and resource consumption is not an issue.

Note that SP3 provides attitude with 10⁻³m precision.

The (timewise) interpolation kernel is only feasible for odd interpolation order (at the moment), for simplicity. The extracted kernel is therefore:

• tmin = (N +1)/2 * τ
• tmax = T(n-1) - (N +1)/2 * τ

with τ the sampling internval, T(n-1) the last epoch provided.

use sp3::prelude::*;
use std::str::FromStr;
use std::path::PathBuf;

let path = PathBuf::new()
    .join(env!("CARGO_MANIFEST_DIR"))
    .join("data/SP3")
    .join("C")
    .join("ESA0OPSRAP_20232390000_01D_15M_ORB.SP3.gz");

let sp3 = SP3::from_gzip_file(&path)
    .unwrap();

let g01 = SV::from_str("G01").unwrap();

// first epoch in this file
let t0 = Epoch::from_str("2023-08-27T00:00:00 GPST")
    .unwrap();

// after 7th epoch we can interpolate by x11 
let t7 = Epoch::from_str("2023-08-27T00:00:00 GPST")
    .unwrap();

let interpolated = sp3.satellite_position_lagrangian_11_interpolation(g01, t0);
assert!(interpolated.is_none(), "too early in this file");

let interpolated = sp3.satellite_position_lagrangian_17_interpolation(g01, t0);
assert!(interpolated.is_none(), "too early in this file");

Satellite clock interpolation

Although it is feasible to interpolate the clock state, it is not recommended to do so. If your processing pipeline requires to interpolate the clock state, you should most likely redesign it or reconsider your dataset.

Clock interpolation should be restricted to short intervals (like 30s at most).

We propose a similar API for clock interpolation as the attitude interpolation.

QC: File Merging

Merge two files together, for example to create a context spanning 48 hours

use std::path::PathBuf;
use sp3::prelude::{SP3, Merge};

let folder = PathBuf::new()
    .join(env!("CARGO_MANIFEST_DIR"))
    .join("data/SP3")
    .join("C");

let sp3_a = folder.clone()
    .join("ESA0OPSRAP_20232390000_01D_15M_ORB.SP3.gz");

let sp3_b = folder.clone()
    .join("ESA0OPSULT_20232320600_02D_15M_ORB.SP3.gz");

let sp3_a = SP3::from_gzip_file(&sp3_a)
    .unwrap();

let sp3_b = SP3::from_gzip_file(&sp3_b)
    .unwrap();

let sp3 = sp3_a.merge(&sp3_b);
assert!(sp3.is_ok());

License

This library is part of the RTK-rs framework which is delivered under the Mozilla V2 Public license.