Category Archive: Datums and Coordinate Systems

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 31 2011

Rescue Your Floating Data


We’ve previously discussed some of the basics of geodesy, ellipsoids and the geoid,  as well as datums and projections. Now, it’s time to pull it all together into what a coordinate system is. Knowing about coordinate systems matters because this is what you interact with inside of a GIS or even CADD currently. Your project …

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May 19 2011

The World is Flat


Yes, the world is still seen as flat in one very common everyday application that nearly every single American uses: a map. If you’re using a GPS system for your car, a CADD or GIS program at work, Mapquest, Bing, or Google Maps, then you’re viewing a flat earth. We are moving closer and closer …

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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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