GroundPolylinePrimitive Not Always Culled (renders through globe)

[timoto]

Using Cesium 1.51

GroundPolylinePrimitive is not always culled as expected and renders through globe.

This example has a single GroundPolylinePrimitive that is clamped to terrain elevation tiles and wraps around the globe: https://dev.globaltimoto.com/

[hpinkos]

Thanks for opening this bug report @timoto! Could you put together a small Sandcastle Code Example to reproduce the error? That would be helpful for us.

This might be related to #4746

[timoto]

Hello @hpinkos

Here is a sandcastle.

[hpinkos]

Thanks @timoto! I'm not sure how soon we'll be able to look into this, but we'll give you an update when we have one. Or if you have time to look into a fix, we're more than happy to review a pull request =)

[timoto]

@hpinkos Thank you for giving this your attention.

I’m sorry but I don’t have the resources to develop a fix myself.

[likangning93]

Line segments on terrain work by drawing a volume into an onscreen polygon, then computing positions on terrain within that onscreen polygon and checking them against a set of 3 planes that slice through the terrain, one for the line width and one for each of the ends. Maybe this culling problem is happening because we aren't bounding the top/bottom of this check, so in some cases the planes slice all the way from one side of the planet to the other.

We could confirm by poking around in PolylineShadowVolumeFS.glsl.

Maybe we can fix this by checking if the position-on-terrain is very far away from one of the volume's positions.

[hpinkos]

I'm no longer able to reproduce this. @timoto if you still see this problem please feel free to re-open this issue. Thanks!