Question

I need an algorithm to figure out if one angle is within a certain amount of degrees from another angle.

My first thought was (a-x < b) && (a+x > b), but it fails when it has to work with angles that wrap around from -179 to 180.

In the diagram above, the region (green) that the angle must be between wraps between the negative and positive sides. How can I determine whether the angle (the red line) falls inside this region?

Answer 1

try this formula:

360-(|a-b|)%360<x || (|a-b|)%360<x

Or, in PHP:

<?php

$b = 10;
$angle1 = -179;
$angle2 = 180;

$diff = $angle1 - $angle2;
if(abs($diff % 360) <= $b || (360-abs($diff % 360))<=$b) {
  echo "yes";
} else {
  echo "no";
}

?>