I have a view direction in 3d space described with 2 values: Horizontal and Vertical (x and y) ranging the full 360 degrees (from -180 to +180), thus describing every possible view direction.
It seems fairly straight forward to me, that the angle between (0,0) and (5,0) would be 5 degrees.
But what is the angle between (0,0) and (5,5). If it was 2 points in 2d I would use Pythagoras theorem; having the difference be sqrt(5^2 + 5^2). But I don't think that would apply in 3d? How do I go about calculating the angle between these 2 directions?
This has likely been asked before, but I probably don't know the correct wording. I assume the "view directions" should be calculated as vectors, but I'm not sure how.