How do I calculate visual angles of objects in vizard?

[lklab]

From wikipedia: "The visual angle is the angle a viewed object subtends at the eye, usually stated in degrees of arc. It also is called the object's angular size."

Heres a diagram:
https://upload.wikimedia.org/wikiped...onDefs.svg.png

Basically I want to find the perceived size of an object in terms of angle occupied in the visual space. I wasn't sure how to calculate this because I don't know how vizard calculates each screen or how the oculus may distort things.

Also, is there an easy way to measure how big an object in vizard is?