How to determine camera tilt or direction relative to the surface?

How can I determine the camera’s direction relative to the surface or center of the Earth?

More specifically I’m interested in determining if the camera is tilted at all relative to the surface of the globe, and by how much.

Ah looks like camera.pitch is what I was looking for. If the camera is straight down, the pitch is -90 degrees. So anything above or below that indicates that the camera is not looking directly at the surface.