Globe underground color

[lilleyse]

Adds globe.undergroundColor and globe.undergroundColorByDistance for controlling how the back side of the globe is rendered when the camera is underground or the globe is translucent.

With the default settings it creates an underground fog type of look

[cesium-concierge]

Thanks for the pull request @lilleyse!

• ✔️ Signed CLA found.

Reviewers, don't forget to make sure that:

• Cesium Viewer works.
• Works in 2D/CV.
• Works (or fails gracefully) in IE11.

[lilleyse]

Feedback from #8726 (comment)

• Rename undergroundColorByDistance to something else
• When above ground, make undergroundColorByDistance relative to globe surface rather than camera

[mramato]

There seems to be a lot of undeground specific properties going in. Should we consider grouping these into their own globe.undeground property for easier documentation and discovery?

[lilleyse]

@mramato that's a good idea, especially for the five new translucency options in #8726. This PR only adds two properties so maybe they can be grouped, but maybe it's not worth the trouble.

[mramato]

Right, I was kind of referring to the effort as a whole (everything going into the next release on June 1st). I haven't spent enough time to understand how many are truly undeground specific, but seems like something we might want to consider looking at.

Another thought, would be whether subsurface makes more sense than undeground? The first includes water, the second is only for the earth. I guess it all depends on how we handle underwater-specific features if/when that happens and if these features are generally meant for "undeground" specifically (maybe they are).

[lilleyse]

These two options are underground specifically. The underground color only shows up once you're below the the bathymetry shell, or the earth is translucent. underwater may have different options.

I need to think more about whether it makes sense to group underground and translucent options together.

[IanLilleyT]

Other than the comments already brought up in the PR, the code looks good

[lilleyse]

• When above ground, make undergroundColorByDistance relative to globe surface rather than camera

Fixed, and in the process created a cool image.

Sandcastle

[lilleyse]

@IanLilleyT updated

[IanLilleyT]

Looks good, thanks @lilleyse !