https://github.com/flightaware/egm2008
Earth Gravitational Model (EGM2008)
https://github.com/flightaware/egm2008
egm2008 geodesy wgs84
Last synced: about 2 months ago
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Earth Gravitational Model (EGM2008)
- Host: GitHub
- URL: https://github.com/flightaware/egm2008
- Owner: flightaware
- License: bsd-3-clause
- Created: 2023-11-01T14:11:25.000Z (over 1 year ago)
- Default Branch: main
- Last Pushed: 2023-11-01T18:15:19.000Z (over 1 year ago)
- Last Synced: 2024-05-04T12:21:48.895Z (about 1 year ago)
- Topics: egm2008, geodesy, wgs84
- Language: Rust
- Homepage: https://crates.io/crates/egm2008
- Size: 30.3 KB
- Stars: 1
- Watchers: 20
- Forks: 0
- Open Issues: 0
-
Metadata Files:
- Readme: README.md
- License: LICENSE.txt
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README
# Earth Gravitational Model (EGM2008)
The coordinate system used by GPS is [WGS 84](https://en.wikipedia.org/wiki/World_Geodetic_System#WGS_84), which expresses altitudes as a "height above ellipsoid".
Because this ellipsoid is a mathematical simplification, the height given by GPS does not necessarily reflect the height above the actual ground beneath.
The [Earth Gravitational Models](https://en.wikipedia.org/wiki/Earth_Gravitational_Model) published by the National Geospatial Intelligence Agency are a way to approximate how high an altitude given in WGS 84 coordinates truly is above the ground.
This library includes data derived from [EGM 2008](https://earth-info.nga.mil/index.php?dir=wgs84&action=wgs84) along with an interpolation function. Together, these allow for an approximate offset to be obtained for arbitrary points on the globe.
## Updating `geoid.rs`
The `src/geoid.rs` file is generated by a Python script (`generate.py`) that
runs NGA's Fortran interpolation program. In order to run the script, you'll
need to download the EGM model data from the NGA's website.
You will also need to install `gfortran`. There are a few ways to do this:
- On macOS, through [Homebrew](https://brew.sh) with `brew install gfortran`.
- Use the included [Nix](https://nix.dev) dev shell with `nix develop`.
For convenience, you can run `generate_geoid.sh` which will download and verify
the model data from NGA, compile the interpolation program, and update
`src/geoid.rs`.