Fix ground atmosphere shaders in 3D orthographic mode

[andrewda]

Description

3D orthographic mode is currently broken with the default globe options (i.e., showGroundAtmosphere = true -- see the Projection sandcastle). The behavior can be fixed by setting showGroundAtmosphere = false. See the attached videos:

Before (showGroundAtmosphere = true)

CleanShot.2025-02-19.at.11.26.20.mp4

Before (showGroundAtmosphere = false)

CleanShot.2025-02-19.at.11.28.42.mp4

This pull request fixes the ground atmosphere shaders so that 3D orthographic mode works by default. See the attached video of this fix, with showGroundAtmosphere = true:

CleanShot.2025-02-19.at.11.28.11.mp4

Issue number and link

#11955

Testing plan

Manual testing with the Projection sandcastle, or with the following code:

const viewer = new Cesium.Viewer("cesiumContainer");

// Setting `showGroundAtmosphere = false` is required for orthographic 3D mode prior to this change
//viewer.scene.globe.showGroundAtmosphere = false;

viewer.scene.camera.switchToOrthographicFrustum();

Author checklist

• I have submitted a Contributor License Agreement
• I have added my name to CONTRIBUTORS.md
• I have updated CHANGES.md with a short summary of my change
• I have added or updated unit tests to ensure consistent code coverage
• I have updated the inline documentation, and included code examples where relevant
• I have performed a self-review of my code

[github-actions]

Thank you for the pull request, @andrewda!

✅ We can confirm we have a CLA on file for you.

[ggetz]

Looks great @andrewda! I was able to confirm the artifacts from #11955 are no longer reproducible in this branch.

Thanks for the fix!