Sphere Earth Conspiracy – Geodesy


This year has seen more then the usual number of references to flat Earth conspiracies in the news Including some very fascinating Twitter tirades. I think thats as good a reason as any to talk about a field of engineering and Earth science that you may have never heard of before. Geodesy Im Grady, and this is Practical Engineering shorts. Where we dip our toes into the pool of technical details behind current events. Or non-events. *Music* How does your airline pilot know which direction to head when they are over the ocean with no landmarks? How do we know the exact boundaries between parcels of land and between states and countries? These are questions which we answer with Geodesy. The science of how we characterise the shape and size of the Earth. You see, it is easy to compare the distance and direction between two locations that are close to one another. But it’s a whole different matter for places that are far apart. Geodesy provides the mathematical frame work we need to make calculations about the globe. And answer questions like, how can a G.P.S. satellite guide me to the nearest taco stand. Well, how can it? You can’t just take a measuring tape between every point on Earth. So to be able to calculate the distance between me and my favourite taco joint. I need to use a coordinate system. For short distances, it’s perfectly fine to assume things are flat and use cartesian coordinates. But over long distances that assumption starts to brake down. Because drawing a straight line between two locations will actually pass through the Earth, rather then along its surface. Flat Earthers say that the Earth is not a sphere. And I have to agree with them on that. In fact if the Earth were a sphere, are lives would almost be as simple as if it were flat. We could use a spherical coordinate system and define location using: Radius, polar angle and azimuth, instead of x and y. Well I did say almost as simple. But the Earth is much bumpier then that, and in fact because of its rotation. The Earth actually bulges along the equator. It’s not a sphere at all. And unfortunately bumpy, bulging coordinate systems make calculating things like distance challenging. If not impossible. So to bridge the cartographic gap between me and delicious tacos we need an idealised model of the Earth. And it turns out that there is a three dimensional shape that matches the Earth fairly well. The oblate spheroid, also known as an ellipsoid. Geodesists have defined a number of reference ellipsoids over the years to try and match the shape of the Earth for use in performing geodetic computations. The reference ellipsoid serves as the basis for the coordinate system which we all know and love. Latitude and longitude. The maths isn’t quite as simple as Cartesian or spherical systems. But it’s much more accurate. In fact the satellites which form the global positioning system or G.P.S. use a reference ellipsoid to calculate a receivers location anywhere on Earth. Mapping software can take data from G.P.S. satellites and perform computations with a very high precision. For example: the distance between me and, well you know. They say that wherever you go, there you are. And no one knows this better then geodesists. They take the irregular, amorphous rock that we live on and give it structure, form and definition. Providing a framework for a whole host of other sciences and technologies. Geodesy tells us that if it looks like an ellipsoid, and spins like an ellipsoid, it might be the Earth. Thank you for watching and let me know what you think. *Music*

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