Question

There are two views:

viewA and viewB. Both are rotated.

The coordinate system for rotation is weird: It goes from 0 to 179,999999 or -179,99999 degrees. So essentially 179,99999 and -179,99999 are very close together!

I want to calculate how much degrees or radians are between these rotations.

For example:

viewA is rotated at 20 degrees

viewB is rotated at 30 degrees

I could just do: rotationB – rotationA = 10.

But the problem with this formula:

viewA is rotated at 179 degrees
viewB is rotated at -179 degrees

that would go wrong: rotationB – rotationA = -179 – 179 = -358

358 is plain wrong, because they are very close together in reality. So one thing I could do maybe is to check if the absolute result value is bigger than 180, and if so, calculate it the other way around to get the short true delta. But I feel this is plain wrong and bad, because of possible floating point errors and unprecision. So if two views are rotated essentially equally at 179,99999999999 degrees I might get a weird 180 or a 0 if I am lucky.

Maybe there’s a genius-style math formular with PI, sine or other useful stuff to get around this problem?

Answer 1

EDIT: Original answer (with Mod) was wrong. would have given 180 – right answer in certain circumstances (angles 30 and -20 for example would give answer of 130, not correct answer of 50):

Two correct answers for all scenarios:

If A1 and A2 are two angles (between -179.99999 and 179.99999,
and Abs means take the Absolute Value,
The angular distance between them, is expressed by:

Angle between = 180 - Abs(Abs(A1 - A2) - 180)

Or, using C-style ternary operator:

Angle between = A1 < 180 + A2? A1 - A2: 360 + A1 - A2