2DView has lower render FPS than 3DView?

1. A concise explanation of the problem you're experiencing.
When I load world contries geojson in 3DView,cesium works well and smoothly.But when I changed to 2DView,it has low FPS.I cann't even wander!Can you tell how to solve the problem?

2. A minimal code example. If you've found a bug, this helps us reproduce and repair it.

3. Context. Why do you need to do this? We might know a better way to accomplish your goal.

4. The Cesium version you're using, your operating system and browser.
My Cesium version is 1.5,OS is windows 7 and Chrome browser.

How big is your GeoJSON? Are you able to share it here or in a Sandcastle example (https://cesiumjs.org/Cesium/Build/Apps/Sandcastle/)?

You can set viewer.scene.debugShowFramesPerSecond = true; to see the frames per second stat. How big of an fps difference do you see between the 3D and 2D views? What I would do is try profiling with something like Chrome’s profiler tool:


To see what’s taking up all this CPU.