How do I calculate the difference of two angle measures?

Question

How can I calculate the difference of two angle measures (given in degrees) in Java so the result is in the range [0°, 180°]?

For example:

350° to 15° = 25°
250° to 190° = 60°

If you're calculating distance, why is the result in degrees? — Buhake Sindi, Sep 27 '11 at 14:29
Can you clarify - are you looking for something built in or are you just asking for a method? also should it take direction into account? Your first example is 25 degrees clockwise and your second is 60 degrees anticlockwise. If you just want the shortest distance then your results should be 0 to 180 (or -180 to 180 if you want to show direction). — Chris, Sep 27 '11 at 14:31
Btw you should not allow 360 because 360 = 0. The domain of the entry arguments should be [0, 360). — m0skit0, Sep 27 '11 at 14:33
Edited for clarity; feel free to roll back if this isn't what you really wanted. — andand, Sep 27 '11 at 15:04

Dmitry Ryadnenko · Accepted Answer · 2018-08-30T07:39:10.837

54

    /**
     * Shortest distance (angular) between two angles.
     * It will be in range [0, 180].
     */
    public static int distance(int alpha, int beta) {
        int phi = Math.abs(beta - alpha) % 360;       // This is either the distance or 360 - distance
        int distance = phi > 180 ? 360 - phi : phi;
        return distance;
    }

edited Aug 30 '18 at 07:39

answered Sep 27 '11 at 14:41

Dmitry Ryadnenko

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and for "Signed difference", append the following code... int sign = (a - b >= 0 && a - b <= 180) || (a - b <= -180 && a- b>= -360) ? 1 : -1; r *= sign; – M. Usman Khan Jun 17 '15 at 09:08
This really helped me, thank you. – Feb 04 '16 at 18:06

M. Usman Khan · Answer 2 · 2017-10-26T03:34:14.813

22

In addition to Nickes answer, if u want "Signed difference"

int d = Math.abs(a - b) % 360; 
int r = d > 180 ? 360 - d : d;

//calculate sign 
int sign = (a - b >= 0 && a - b <= 180) || (a - b <=-180 && a- b>= -360) ? 1 : -1; 
r *= sign;

EDITED:

Where 'a' and 'b' are two angles to find the difference of.

'd' is difference. 'r' is result / final difference.

edited Oct 26 '17 at 03:34

answered Jun 17 '15 at 09:11

M. Usman Khan

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What do `d` and `r` represent in this context? Difference and rotation? – Stevoisiak Apr 26 '17 at 22:05
1

I assume `a` and `b` represent `targetAngle` and `currentAngle` respectively. – Stevoisiak Apr 27 '17 at 00:02
@StevenVascellaro yes that's right – M. Usman Khan Apr 27 '17 at 02:22
This does not work properly for negative angles. For instance, the sign between 0 and -380 is negative, but the sign between 0 and -20 is positive. Easy fix is to set a=(a+360)%360, b=(b+360)%360. This won't work for angles that are below -360 though. – JSideris Jul 21 '17 at 17:26
Had a night to think about it. Make all angles (a and b) positive before calculating sign by doing the following: `if(a < 0) a = 360 - ((-a) % 360);` `else a = a % 360;` – JSideris Jul 22 '17 at 22:42
@StevenVascellaro thanks for pointing out. I have added the details to my answer. – M. Usman Khan Oct 26 '17 at 03:34
@usman Why not use self-descriptive variable names instead? – Stevoisiak Oct 26 '17 at 03:49

score 8 · Answer 3 · answered Sep 27 '11 at 14:33

8

Just take the absolute value of their difference, then, if larger than 180, substract 360° and take the absolute value of the result.

answered Sep 27 '11 at 14:33

JB Nizet

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Artefacto · Answer 4 · 2011-09-27T14:37:20.933

5

Just do

(15 - 350) % 360

If the direction doesn't matter (you want the one that yields the smallest value), then do the reverse subtraction (mod 360) and calculate the smallest value of the two (e.g. with Math.min).

edited Sep 27 '11 at 14:37

answered Sep 27 '11 at 14:31

Artefacto

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can you explain a little more? i dont understand you "then do the reverse subtraction (mod 360) and calculate the smallest value." – NullPointerException Sep 27 '11 at 14:38
@And I mean doing also (350 - 15) % 360. – Artefacto Sep 27 '11 at 14:46
min((a-b)%360, (b-a)%360) @AndroidUser99 – squid Jun 27 '15 at 15:00
@Artefacto Can you append an example of "Reverse subtraction" to your answer for a non-direction specific answer? – Stevoisiak Apr 26 '17 at 22:02

score 4 · Answer 5 · answered Sep 27 '11 at 14:32

4

How about the following:

dist = (a - b + 360) % 360;
if (dist > 180) dist = 360 - dist;

answered Sep 27 '11 at 14:32

NPE

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score 1 · Answer 6 · edited Mar 18 '20 at 09:56

1

diff = MAX(angle1, angle2) - MIN(angle1, angle2);  
if (diff > 180) diff = 360 - diff;

edited Mar 18 '20 at 09:56

N3R4ZZuRR0

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answered Oct 09 '11 at 22:39

Oliver

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How do I calculate the difference of two angle measures?

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