Ellipsoid-scaled Earth-centered Fixed frame.

CesiumJS
1

Hi,

In the documentation of quantized meshes (http://cesiumjs.org/data-and-assets/terrain/formats/quantized-mesh-1.0.html) it is stated that the Horizon occlusion point is expressed in ellipsoid-scaled earth-centered fixed frame coordinates. What are those exactly?

Ty

2

Hi,

Ellipsoid-scaled coordinates are described near the end of this blog post, in the section title “Generalizing to an Ellipsoid”:

https://cesiumjs.org/2013/04/25/Horizon-culling/

If you’re computing the horizon occlusion point, you’ll probably want to read that blog post and the followup:

https://cesiumjs.org/2013/05/09/Computing-the-horizon-occlusion-point/

The short version of ellipsoid-scaled coordinates is this: take regular Earth-centered Earth-fixed coordinates, and multiply each component by one over the corresponding ellipsoid radii. Here’s the implementation of that in Cesium:

https://github.com/AnalyticalGraphicsInc/cesium/blob/8db80fb9b12cfaa1d572143133619f782c8ee89c/Source/Core/Ellipsoid.js#L644

By the way, AGI guys, the math in the blog posts above is broken because the CDN URL of MathJax changed. Could you guys update it when you get a chance? The new URL is:

https://cdn.mathjax.org/mathjax/​latest/MathJax.js?config=TeX-AMS-MML_HTMLorMML

Kevin

3

While both the old links and new links worked fine for me, I updated the pages to use the new links. It will go out with 1.6

4

Thank you very much, that was very helpful.

FD.