Convert standard 360-degree to atan2

Question

I need to reverse calculation of standard 360 angle to atan2.

It's my standard angle calulation

Standard angle =  (int) Math.toDegrees(Math.atan2(y,x));

if(angle < 0)
  angle += 360;

I need Math.atan2 value from angle how to achieve that.

And what result do you want? Two coordinates or angle in range -Pi..Pi? — MBo, Sep 12 '16 at 07:08
What programming language is this? Is this Java? Please tag your question with the language in use. To update your question, click on the "[edit]" link under the post. Thank you. — Pang, Sep 14 '16 at 02:42

MBo · Answer 1 · 2016-09-12T07:44:04.320

2

To translate degrees range 0..360 into radians range -Pi..Pi:

if(angle > 180)
   angle -= 360;
angle_radians = Math.toRadians(angle);

If your angle may be beyond standard range (you did not mentioned this), use integer modulo instead of loops

angle = angle % 360

(check how modulo operator works with negative numbers in your language)

edited Sep 12 '16 at 07:44

answered Sep 12 '16 at 07:22

MBo

77,366
5
53
86

score 1 · Answer 2 · answered Sep 12 '16 at 08:46

Though your question is not very clear, it seems that you want to retrieve the angle before the statement

if (angle < 0)
  angle += 360;

As atan2 returns a value in the range [-π,π), i.e. [-180°,180°), the subrange [-180°,0°) is mapped to [180°,360°). Then you invert with

if (angle >= 180°)
  angle-= 360;

You also need to convert back to radians.

andand · Answer 3 · 2016-09-12T17:22:23.833

A general solution with O(1) performance:

double generalModulus(double value, double modulus, double offset) {
    return value - Math.floor((value-offset)/modulus) * modulus + offset;
}

double normalizeAngleDegrees(double angleInDegrees, double offset) {
    return generalModulus(angleInDegrees, 360.0, offset);
}

double normalizeAngleRadians(double angleInRadians, double offset) {
    return generalModulus(angleInRadians, 2.0*Math.PI, offset);
}

To use:

double normDeg = normalizeAngleDegrees(angle, -180); // produces angle in range [-180, 180)
double normRad = normalizeAngleRadians(angle, 0); // produces angle in range [0, 2*Pi)

score -1 · Answer 4 · answered Sep 12 '16 at 07:29

-1

My Own answer

int normalizeAngle(int angle)
{
    int newAngle = angle;
    while (newAngle <= -180) newAngle += 360;
    while (newAngle > 180) newAngle -= 360;
    return newAngle;
}

answered Sep 12 '16 at 07:29

sabish

31
1
8

Look at my addition – MBo Sep 12 '16 at 07:46

Convert standard 360-degree to atan2

4 Answers4