scene.sampleHeight cause polygon(clamp to ground) to flicker at top view

[JiaoJianing]

What happened?

I want to draw a midpoint between two points, and I expect the point height fit the ground/3dtiles. I first calculate the world position of that point, convert it to cartographic coordinate, then call scene.sampleHeight. When at a top view, the polygon will flicker.It seems that sampleHeight destroy the main render.

https://github.com/CesiumGS/cesium/assets/12868409/56826d83-ff50-4cf2-8878-61f8dd12179e

Reproduction steps

1.Create a polygon and clamp it to ground; 2.Change the camera to a top view; 3.Call scene.sampleHeight; 4.The polygon flicker.

Sandcastle example

https://sandcastle.cesium.com/#c=fVNba9swGP0rIk8OeIou1i1Nw0opW2F0kJW9LHtQHTURUywjKSlp6X+fEse9U7DB0vnOOd/NAABQ+yYmsLXmzgRwChpzB85NtJs1/H24K+aD+nA+903StjFhPhiezJtMBc4k0KLXrHMdUv7SDS2+YI4QriiUvFJKiYryEjBKMJUMSqoEEhhVJaCYoEoiyCjnHDMq6SsD/IkBU0IRDnEW46KqSHUwoIIiKCXChFVS7Q2w4LSCqkKKkwpj9sqAfFoBwVJCxITKUkwd9AllCkoic7aUyU5fSAEZYphyIshLeR32ff3TojKXkl/yd950aNd0aJpkkzUR6sWieOggABq9NmMwH8zMArTe7Za+AfmJm3CrazMflH3gERyDJyoAK2uCDvVqN97bl8/AWicTrHbjp2K98wF+m11cXME7m1Znrl3pIs9i+IJVOx2jvbW1TtY317vWPPPfQfD6YjY7u7zq6Y9Hoce+Kcey771fX/viTRP2QV1YNOmyydlutSuKITidPhe4b2udp+TfD84vg25Xti5w3jrCuZBMMkUQF6wEuSycV0ApRikSAhFSAsIZpJxhzEkOQ6rq0+xsgokbl7LPMc9Ym8bAqNetM9+NXa5SccikZz2WACOEhieDcjCJaefMtJf7atetDwlsgisgHCWTNfI44uhmU/8zCdYx9iqT0UvqZGG3wC5OP/gTu9Fk5Hbj3C97nxdjOhnl+HdU5/XCNsufWxOc3u3DVnj6o7uEEE5G+fgxM3nvbnR4o/wf

Environment

Browser:Chrome CesiumJS Version:1.118 Operating System:Windows 10 x64

[ggetz]

Interesting, I'm not able to reproduce on my machine.

Would you mind leaving the Chrome version you're seeing this on? Also, could you please visit webglreport.com and take a screenshot of your results?

Thanks!

[GatorScott]

@ggetz, I was able to reproduce by using <CTRL><MB1> dragging until view was directly above triangle (Edge Version 125.0.2535.85 (Official build) (64-bit)).

[GatorScott]

Also in Chrome Version 125.0.6422.142 (Official Build) (64-bit), both on Windows 10.

[ggetz]

Thanks @GatorScott! I see the issue know. It looks like it may be an issue with the shadow volumes used for ground primitives.

[CommName]

I experience the same problem, but it instead of flickering it cuts the polygon entirely since I am using it in CallBackProperty / onTick event

[jjspace]

Also reported in https://github.com/CesiumGS/cesium/issues/12381 and https://github.com/CesiumGS/cesium/issues/12221

[AllenLmz]

It seems to be an issue where polygon renders first, followed by terrain. Immediately after executing scene.sampleHeight, polygon is not on the surface of terrain. I added a line of code viewer.scene.render(viewer.clock.currentTime); after scene.sampleHeight execution, which temporarily resolved the issue