Tag Archive: ellipsoid

Jun 02 2011

The Vertical Side of Things

A vertical datum is defined by the measured gravity anomalies between ellipsoid and geoid. But it’s not quite that simple. Between understanding mean low water versus mean high water versus mean low low water versus mean sea level, this area can get very dangerous. On top of that you have other things to complicate the …

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May 17 2011

Where am I?


“It is clear that the earth does not move, and that it does not lie elsewhere than at the center.”                 – Aristotle (one of first to estimate size of the earth, On the Heavens, p54) We’ve talked a little about geodesy and reference ellipsoids but what is a datum? It’s pretty simple, actually. A datum …

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May 12 2011

This isn’t a Bowling Ball

Planet Earth Bowling Ball

even the most mathematically sophisticated geoid can only approximate the real shape of the earth.                          – Witold Fraczek The earth is hardly a nice sphere like a bowling ball or even a nice simple spheroid. All of our models of the earth are …

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