While rendering some fairly basic primitives, I’m getting a strange artifact that looks like there’s something slicing through the geometries.
With terrain on, a similar thing happens, but it’s more obvious as the terrain appears to cut through the 2D geometry too.
It appears as a line whose width and angle are dependent on the position of the camera. The width of the line seems to increase as the gets higher (or as I middle-click pan up and tilt down), it’s always perpendicular to the direction of the camera across the plane of the ellipsoid, and as I zoom in it gets further away.
Do you know what this might be? Have we set something up incorrectly?
We’re creating the geometries like:
var poly = new Cesium.GeometryInstance({
geometry: new Cesium.PolygonGeometry({
polygonHierarchy: { positions: vertices },
height: height
}),
id: args.id,
attributes: {
color: Cesium.ColorGeometryInstanceAttribute.fromColor(DEFAULT_COLOR)
}
});
Then wrap that in a primitive:
new Primitive({
geometryInstances: poly,
appearance: new Cesium.EllipsoidSurfaceAppearance()
});
scene.getPrimitives().add(primitive);
I’ve done some work cleaning up our primitive creation, but the problem remains. We now create geometry with:
new GeometryInstance({
id: parseInt(args.id),
geometry: new Cesium.PolygonGeometry({
polygonHierarchy: {positions: vertices},
height: minTerrainHeight + altitude,
extrudedHeight: minTerrainHeight + altitude + extrusionHeight
})
});
And primitives with:
if (!is3d) {
appearance = new Cesium.EllipsoidSurfaceAppearance();
} else {
appearance = new Cesium.MaterialAppearance({closed: true, flat: true});
}
appearance.material.uniforms.color = color;
The artifact doesn’t appear to affect the 2D geometries with the EllipsoidSurfaceAppearance.
Hi Oliver,
Your code is OK. This is a known-issue with translucent objects due to how we eliminate z-fighting for massive view distances. Opaque objects do not have this artifact. If you are curious about the details, see these slides (Slides 29 and 30 in particular):
Cesium: The Platform for 3D Geospatial
We can minimize the artifact a bit more by reducing frustum overlap, but fully eliminating it in the general case is hard. Recently, I almost solved it with stenciling, but it didn’t turn out as expected. I hope to think about it again, but it will be a few months out.
As for the screenshot with terrain, Kevin may have more to add.
Patrick
