CODEWITHSUNDEEP
mathgeometrybearing
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Reputation: 7

What is the mathematical way to determine an angle from two given true bearings?

Given that I have two true bearings as a start bearing 315 degrees and an end bearing 45 degrees, is there a better way to determine the angle between the two true bearings? The complication comes in when the start bearing is greater than the end bearing. I have the following that works but I figure there is a better/mathematical way.

double tStartBearing = 315;
double tEndBearing = 45;
double tAngle;

if (tStartBearing > tEndBearing) {
   tAngle = tStartBearing - tEndBearing - 180;
} else {
   tAngle = tEndBearing - tStartBearing;
}

Expect the resulting value of tAngle to be 90. Consider a start bearing of 0 and an end bearing of 359.9, the resulting value of tAngle should be 359.9, not 0.1.

Upvotes: 0

Views: 326

Answers (1)

dxiv
dxiv

Reputation: 17668

The (signed) angle is always end - start. Assuming the start and end angles are both in the same range [n, n + 360), their difference will be between (-360, 360).

To normalize the difference to a positive angle in the range [0, 360), use:

tAngle = (tEndBearing - tStartBearing + 360) % 360;

To normalize the difference to a signed angle in the range [-180, 180), instead, use:

tAngle = (tEndBearing - tStartBearing + 360 + 180) % 360 - 180;

The above work whether the start angle is smaller than the end one, or the other way around.

Upvotes: 2

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