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Brion Vibber :blobcatcoffee: (brion@bikeshed.vibber.net)'s status on Monday, 09-Jan-2023 16:19:43 JST Brion Vibber :blobcatcoffee:

People think of GPS as giving lat/lon coords, but it actually calculates X/Y/Z relative to the center of the Earth, then converts them according to the WGS84 datum[1] into lat/lon and altitude.
However in aviation, the primary altitude measure for navigation remains the classic barometric pressure-based altimeter.
At lower altitudes, you calibrate the instrument relative to readings from a local airfield; at higher altitudes everyone uses a standard calibration.
[1] https://en.wikipedia.org/wiki/World_Geodetic_System
In conversation Monday, 09-Jan-2023 16:19:43 JST from bikeshed.vibber.net permalink
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  World Geodetic System
  
  The World Geodetic System (WGS) is a standard used in cartography, geodesy, and satellite navigation including GPS. The current version, WGS 84, defines an Earth-centered, Earth-fixed coordinate system and a geodetic datum, and also describes the associated Earth Gravitational Model (EGM) and World Magnetic Model (WMM). The standard is published and maintained by the United States National Geospatial-Intelligence Agency. History Efforts to supplement the various national surveying systems began in the 19th century with F.R. Helmert's famous book Mathematische und Physikalische Theorien der Physikalischen Geodäsie (Mathematical and Physical Theories of Physical Geodesy). Austria and Germany founded the Zentralbüro für die Internationale Erdmessung (Central Bureau of International Geodesy), and a series of global ellipsoids of the Earth were derived (e.g., Helmert 1906, Hayford 1910/ 1924). A unified geodetic system for the whole world became essential in the 1950s for several reasons: International space science and the beginning...
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  Alexandre Oliva (lxo@gnusocial.net)'s status on Monday, 09-Jan-2023 16:19:41 JST Alexandre Oliva
  in reply to
  
  funny, this crossed my diaspora timeline yesterday
  https://en.wikipedia.org/wiki/Gladys_West
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    Gladys West
    
    Gladys Mae West (née Brown; born October 27, 1930) is an American mathematician known for her contributions to the mathematical modeling of the shape of the Earth, and her work on the development of the satellite geodesy models that were eventually incorporated into the Global Positioning System (GPS). West was inducted into the United States Air Force Hall of Fame in 2018. West was awarded the Webby Lifetime Achievement Award at 25th Annual Webby Awards for the development of the satellite geodesy models. Early life and education West was born as Gladys Mae Brown in Sutherland, Virginia, in Dinwiddie County, a rural county south of Richmond. Her family was an African-American farming family in a community of sharecroppers. She spent much of her childhood working on her family's small farm. Her mother worked at a tobacco factory. Her father was a farmer who also worked for the railroad. West realized early on that she did not want to work in the tobacco fields or factories like the rest of her family, and decided that education would be her way out.When West was on her...
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  Brion Vibber :blobcatcoffee: (brion@bikeshed.vibber.net)'s status on Monday, 09-Jan-2023 16:19:42 JST Brion Vibber :blobcatcoffee:
  in reply to
  - Dr. Eric J. Fielding, PhD
  @EricFielding I just love that this wild relativistic physics + rocketry + radio technology is just so casually *available* to us :D
  lotta work went into that stuff
  
  In conversation Monday, 09-Jan-2023 16:19:42 JST permalink
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  Dr. Eric J. Fielding, PhD (ericfielding@mastodon.social)'s status on Monday, 09-Jan-2023 16:19:43 JST Dr. Eric J. Fielding, PhD
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  @brion Minor quibble: The GPS or GNSS locations are calculated relative to the center of the Earth in an exterior reference frame estimated from information about the GNSS satellite orbits and then converted to locations relative to the rotating Earth with an Earth rotation model at a specific time. This is a small issue for airplane-scale navigation but important for precise locations.
  
  In conversation Monday, 09-Jan-2023 16:19:43 JST permalink

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