3D Selection with Orthographic Camera

I have a 3D object and I need to be able to select a region and make that disappear. Can someone tell me or point me to resources that explain how to do a selection with an orthographic camera. I see tons of information about perspective camera but nothing about orthographic.

How about using simple raycasting to select parts of a mesh? This approach works like when using a perspective camera. There is actually a separate example for this on the homepage: