Why does my polyline primitive's depthFailAppearance trigger depending on zoom level of a camera?

CesiumJS
1

Hi,

I create my primitives the following way:

When my zoom level is close to the surface, it seems to test the depth of the polyline and use the depthFail appearance (-100m Boston):

image
image1920×746 93.4 KB

However, if I zoom my camera out, the polylines become solid.

image
image1920×885 149 KB

Why is it happening? Is there some parameter that is responsible for using depth test or not?

2

Hi @ddaddadda, do you want to make the polyline always visible? If so, you can simply turn off the depth test in the polyline appearance.

const appearance = new Cesium.PolylineColorAppearance({
  translucent: false,
  renderState: {
    depthTest: {
      enabled: false,  // shut off depth test
    },
  },
});

Here is a modified Sandcastle demonstrating this approach.

If you want the part of the polygon below the surface to be properly occluded based on the depth value at different points, it will be more difficult. When zoomed out, -100m is small relative to the depths in the scene, so the depth buffer may not have enough precision for an accurate depth test. One option would be to split the polyline into above- and below-ground segments by pre-computing the points where the line intersects the surface.

3

Unfortunately, I want the polygon below the surface to render with a different appearance :slight_smile: .

4

Hi @ddaddadda,

Do you have an idea of how close (in meters) the camera is to the line before the depthFailAppearance works as you expect?

You may need to pre-compute the points where the line intersects the surface, and perhaps split the line into separate Polylines with different appearances. The depth buffer is single-precision at best, or worse in many cases. When zoomed out, small differences won’t be resolvable via standard depth testing.