But we want to do more than that, and dealing with elevation can be surprisingly complex and fragile. Imagine you are building an offshore wind turbine. You w

But we want to do more than that, and dealing with elevation can be surprisingly complex and fragile. Imagine you are building an offshore wind turbine. You want 20m of clearance between the sea and turbine blade. That means 20m above highest possible tide. Tidal data is only available for a port 200 miles away and will be different for you based on local gravity. So you use modelling from satellite based gravity data to make an assumption. And then give instructions to a ship out at sea who has a contractual obligation to place the turbine within 30cm of the required position. Which coordinate system do you use? And when you are modelling a microwave link from that turbine to an onshore location on the horizon that is surveyed using a local datum what coordinate system do you use? In reality geocentric coordinates are unlikely to be used. But maybe it would be easier if they could be. The world it not flat and it is not easily modelled as a sphere. A set of coordinates always carry with them a set of assumptions that may not work with your particular task. Geocentric coords can remove some of those assumptions.