How can I export NavMesh Data

I’m having trouble exporting data from NavMesh.
I want to extract the triangle data (v and f) from the green area (navigation) that is displayed in the Unreal Engine Editor.

So in the NavMesh settings, I set the Runtime Generation option to Dynamic and wrote the following code.

However, the obj file output via ExportNavigationData() contains the entire map outside of the green area, and the triangle tiles don’t appear to be the size I want.

If anyone has a solution for this, I would appreciate a detailed response.