https://github.com/iannesbitt/pyegt

Ellipsoid-relative geoid and tidal model height lookup
https://github.com/iannesbitt/pyegt

ellipsoid-height geoid noaa-api noaa-ngs tidal-model

Last synced: 3 months ago
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Ellipsoid-relative geoid and tidal model height lookup

• Host: GitHub
• URL: https://github.com/iannesbitt/pyegt
• Owner: iannesbitt
• License: apache-2.0
• Created: 2023-06-15T22:14:23.000Z (about 2 years ago)
• Default Branch: main
• Last Pushed: 2023-11-02T20:45:56.000Z (over 1 year ago)
• Last Synced: 2025-03-08T11:08:41.878Z (3 months ago)
• Topics: ellipsoid-height, geoid, noaa-api, noaa-ngs, tidal-model
• Language: HTML
• Homepage: https://iannesbitt.github.io/pyegt
• Size: 6.83 MB
• Stars: 0
• Watchers: 1
• Forks: 0
• Open Issues: 0
• Metadata Files:
  • Readme: README.md
  • Changelog: CHANGES.md
  • License: LICENSE

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README

        
# pyegt

**Ellipsoid-relative geoid and tidal model height lookup**

*Ian Nesbitt, NCEAS-UCSB*

[![PyPI](https://img.shields.io/pypi/v/pyegt)](https://pypi.org/project/pyegt)

[![Conda](https://img.shields.io/conda/v/iannesbitt/pyegt)](https://anaconda.org/iannesbitt/pyegt)

[![Docs](https://img.shields.io/github/deployments/iannesbitt/pyegt/github-pages?label=docs)](https://iannesbitt.github.io/pyegt)

`pyegt` is an open source program developed by [NCEAS](https://nceas.ucsb.edu)

to look up the geoid, tidal, or geopotential model height above the ellipsoid

in order to convert model-referenced heights to ellipsoid height (i.e.

compatible with [Cesium](https://cesium.com)) and vice-versa.

## About

The following figure demonstrates the difference between geoid, ellipsoid,

and topographic ground surface:

![Ellipsoid, geoid, and topography](https://user-images.githubusercontent.com/18689918/239385604-5b5dd0df-e2fb-4ea9-90e7-575287a069e6.png)

The figure shows a diagram with a conceptual model of ellipsoid height `h`, geoid

height `H`, and height of geoid relative to ellipsoid `N`

along with topographic surface (grey).

Ellipsoidal height (`h`) is generally used in global projections such as

Cesium due to its small digital footprint and ease of calculation relative

to systems based on gravity or geopotential height. However, gravity and

tides are influenced by local differences in Earth's density and other

factors. Therefore some projects prefer reference systems that use height

referenced to a geoid or tidal model (`H`) which provides a much easier

framework to understand height relative to, for example, modeled mean sea

level or sea level potential. Converting from `H` to `h` requires

knowing the height difference between the geoid and the ellipsoid (`N`).

Conversion is then a simple addition of these values (`H + N = h`).

## Usage

```python

>>> from pyegt.height import HeightModel

>>> h = HeightModel(lat=44.256616, lon=-73.964784, from_model='GEOID12B')

>>> repr(h)

HeightModel(lat=44.256616, lon=-73.964784, from_model='GEOID12B', region='None') -> -28.157 meters

>>> float(h)

-28.157

>>> h.in_feet_us_survey()

-92.37842416572809

```