anyone can explain the "field of view"

Question

In graphics software, sometimes we saw "field of view" for camera. Can someone explain what does it mean?

Answer 1

The field of view (in the gluPerspective call) is the angle in degrees between a plane which passes through the camera position and the top of your screen and another plane which passes through the camera position and the bottom of your screen.

Edit: Since you need not have a full-screen viewport: Any line which is projected to (x1, 0)-(x2, 0) lies in the first plane, any line that is projected to (x3, height)-(x4, height) lies in the second, where height is the height of your viewport in pixels.