Airport elevation wrong?

CesiumJS
1

Hello,

Sorry if I’m in the wrong category. I’m using https://sandcastle.cesium.com/?src=3D%20Models.html to test my flight tracking program. The GPS coordinates are accurate. But the height, in this case 207 is off. 207 is the field elevation for Kuwait International Airport . But why is it this showing the 3D airplane hovering?

But if I type in 0 for height, it seem level to the ground.

okbk
okbk396×293 42.2 KB

const position = Cesium.Cartesian3.fromDegrees(
     47.971,29.223,
    207,
  );

Thanks,

Tony

2

(I moved this into the CesiumJS section - I think that this might fit better)

The height above sea level of the Kuwait International Airport is said to be 204 feet according to Wikipedia, which is roughly 62 meters. (Note that the units in CesiumJS are generally meters)

This may be one reason for the unexpected result. The other one is that by default, CesiumJS does not “know” that this airport has this specific height. By default, CesiumJS basically displays a textured ellipsoid.

Some technical background can be found in the Geospatial Guide, e.g. What is the shape of the earth? and What is Mean Sea Level (MSL)?. The short version is: It’s complicated :slight_smile:

If you had a “real 3D model” of the airport itself, then this could reflect this height of 62 meters. Depending on the exact use case, you could consider taking the “real” offset of the GPS coordinates (i.e. 62 meters) into account, and subtract that from the visual representation, i.e. when displaying the plane on the ellipsoid.

One could be tempted to just use an existing terrain representation here - something that more closely approximates the real height. In the follwing sandcastle, the “Cesium World Terrain” is enabled:

… but you can see that

  1. the world is bumpy - it is still only an approximation, and has to include everything between the Dead Sea and Mount Everest…
  2. the height that I used there (33 meters) still does not match the value of 62 meters that one might expect. (I’m not even sure whether the whole airport can have this exact height…)
3

Thank you