1. A concise explanation of the problem you're experiencing.
I want to analysis visibility between two points,but i can't get the triangles of the primitives.
Cesium version is:"1.49"
I’m not sure entirely what kind of analysis you mean, but the Cesium ion SDK does have some built in visibility analysis tools. If you’re interested in trying those reach out to Tim (tim@cesium.com).
You can see what this looks like at the beginning of this video: