Astrodynamics coordinate frame transforms
Unified Satellite.v with optional ~propagate
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README.md
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README.md
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# coordinate
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Astrodynamics coordinate frame transforms.
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Conversions between standard reference frames used in satellite operations: TEME (SGP4 output), ECEF (Earth-fixed), J2000/EME2000 (inertial), and geodetic (lat/lon/alt). Includes WGS-84 constants and GMST computation.
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## Installation
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```
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opam install coordinate
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```
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## Usage
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```ocaml
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(* Convert SGP4 TEME output to geodetic coordinates *)
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let gmst = Coordinate.gmst_of_unix unix_time in
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let ecef = Coordinate.teme_to_ecef ~gmst teme_pos in
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let geo = Coordinate.ecef_to_geodetic ecef in
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Printf.printf "Lat: %.4f Lon: %.4f Alt: %.1f km\n" geo.lat geo.lon geo.alt
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```
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## API Overview
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- **`type vec3`** -- Cartesian position/velocity vector (km or km/s)
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- **`type geodetic`** -- `lat` (deg), `lon` (deg), `alt` (km)
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- **`earth_radius`**, **`earth_mu`**, **`earth_j2`** -- WGS-84 constants
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- **`gmst_of_unix`**, **`gmst`** -- Greenwich Mean Sidereal Time (IAU 1982)
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- **`teme_to_ecef`**, **`ecef_to_teme`** -- TEME/ECEF rotation via GMST
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- **`j2000_to_ecef`**, **`ecef_to_j2000`** -- J2000/ECEF rotation
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- **`ecef_to_geodetic`** -- Bowring's iterative method on WGS-84 ellipsoid
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- **`geodetic_to_ecef`** -- Geodetic to ECEF
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- **`teme_to_geodetic`** -- TEME to geodetic (convenience)
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## License
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ISC
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test/test_coordinate.ml
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test/test_coordinate.ml
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let g = Coordinate.ecef_to_geodetic v in
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(* Approximate — the example uses a different reference ellipsoid *)
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let r = Coordinate.vec3_length v in
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let expected_r =
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sqrt
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((6524.834 *. 6524.834) +. (6862.875 *. 6862.875) +. (6448.296 *. 6448.296)
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)
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in
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Alcotest.(check (float 0.1)) "radius" expected_r r;
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Alcotest.(check (float 2.0)) "lat ~34" 34. g.lat;
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Alcotest.(check (float 200.)) "alt ~5000" 5000. g.alt
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Alcotest.(check (float 0.001)) "radius" 11456.572 r;
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Alcotest.(check (float 0.5)) "lat" 34.25 g.lat;
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Alcotest.(check (float 50.)) "alt" 5078. g.alt
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(* ================================================================== *)
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(* TEME → Geodetic (full pipeline) *)