Getting the shortest angle path

Question

I need to get the shortest direction between two angles. Like if Ang1 is 5 and Ang2 is 355 then I want it to return that I need to subtract from Ang1 to get to Ang2 .

I have some code that will tell me the shortest distance, but not the shortest direction.

function getShortAngle(a1, a2) {

    let angle = (Math.abs(a1 - a2))%360;

    if(angle > 180)
        angle = 360 - angle;

    return angle;
};

console.log(getShortAngle(360, 720));

Or in Smallbasic:

Sub GetShortestpath

    angle = Math.Remainder((Math.abs(a1 - a2)),360)

    if angle > 180 Then
        angle = 360 - angle
    EndIf

    Return = angle
EndSub

Thanks for any help!

Answer 1

Surely that's just setting the direction based on which angle you choose.

If you're working out the angle/direction from a1 to a2, the following pseudo-code should give you what you need:

# precondition: [a1,a2] >= 0
angle = ((a2 % 360) - (a1 % 360) + 360) % 360
direction = CLOCKWISE
if angle > 180:
    angle = 360 - angle
    direction = ANTICLOCKWISE

In cases where the difference is exactly 180°, it prefers the clockwise direction.

Forgive the complex expression getting the angle, it just to ensure you get a value 0 through 359 regardless of the relative positions and workings of your modulo operator with negative numbers.

You can greately simplify it if you make the precondition more restrictive, ensuring a1 and a2 are limited to the range 0..359:

# precondition: 0 <= [a1,a2] <= 359
angle = (a2 - a1 + 360) % 360