fix bounding volumes for hemisphere-size GroundPolylineGeometry

[likangning93]

Fixes #7043

Here's a primitive-based version of what was noted in the issue on the current release Sandcastle.

For comparison, in this branch's Sandcastle.

The problem was in how the bounding sphere was getting computed - the new method is simpler and should work for all cases. The bounding sphere doesn't necessarily cover the shadow volume for very short polylines in some places anymore, but those shadow volumes are extremely conservative, so in practice it shouldn't be a problem, it still covers the lines on terrain and on the ellipsoid.

Here's the spec case, roughly:

var viewer = new Cesium.Viewer('cesiumContainer');

var positions = Cesium.Cartesian3.fromDegreesArray([
    -122.17580380403314, 46.19984918190237,
    -122.17581380403314, 46.19984918190237
]);

var instance = new Cesium.GeometryInstance({
    geometry : new Cesium.GroundPolylineGeometry({
        positions : positions,
        loop : true,
        width : 8.0
    })
});

var polylineOnTerrainPrimitive = new Cesium.GroundPolylinePrimitive({
    geometryInstances : [instance],
    debugShowShadowVolume : false,
    debugShowBoundingVolume : true,
});
viewer.scene.groundPrimitives.add(polylineOnTerrainPrimitive);

viewer.camera.lookAt(positions[1], new Cesium.Cartesian3(100.0, 100.0, 100.0));
viewer.camera.lookAtTransform(Cesium.Matrix4.IDENTITY);

[cesium-concierge]

Thanks for the pull request @likangning93!

• ✔️ Signed CLA found.
• ❔ CHANGES.md was not updated.
  • If this change updates the public API in any way, please add a bullet point to CHANGES.md.

Reviewers, don't forget to make sure that:

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

---

I am a bot who helps you make Cesium awesome! Contributions to my configuration are welcome.

🌍 🌎 🌏

[hpinkos]

Looks great @likangning93! This fixes the very large polyline case, and still has roughly the same bounding sphere for very small polylines.