What is a Reference Ellipsoid and How It Models the Earth's Shape
The earth is not a perfect sphere. It bulges slightly at the equator and flattens slightly at the poles due to its own rotation. A reference ellipsoid is the mathematical model that captures this shape precisely enough for GPS and coordinate systems to calculate positions accurately anywhere on the planet.
The earth's true shape never changes, unlike this sky, but the mathematical model we use to describe it has been refined many times over the decades.
Why a Perfect Sphere Would Not Work
WGS84: The Ellipsoid GPS Actually Uses
Every GPS satellite calculates position using the same shared WGS84 ellipsoid model, keeping the entire global system consistent.
| Parameter | WGS84 Value |
|---|---|
| Equatorial radius | 6,378.137 km |
| Polar radius | 6,356.752 km |
| Flattening | Approximately 1 part in 298 |
The Ellipsoid is Only the Starting Point
Understanding this mathematical foundation explains why every GPS coordinate ultimately traces back to a shared, precisely defined model, ensuring consistency across every survey instrument and platform globally. Learn more about our DGPS survey services.
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