Elevation correction and the geoid tutorial
https://www.unavco.org/education/education-resources/tutorials/the-shape-of-earth-and-reference-ellipsoids/

UNAVCO


The Earth is not a perfect sphere, but is instead more like a slightly squashed sphere called an ellipsoid. Because of this, GPS receivers must use a correction model (called a geoid) to calculate true elevation above sea level. UNAVCO has prepared this explanation for both teachers and students to learn more about accuracy, scientific models, and how GPS receivers work.


Subject: Geography:Geospatial, Geoscience:Geology:Geophysics:Geodesy
Resource Type: Scientific Resources:Overview/Reference Work
Theme: Teach the Earth:Course Topics:Geodesy, GIS/Remote Sensing, Geophysics