CODEWITHSUNDEEP
javascript
Strawberry
Strawberry

Reputation: 67928

How do you compare radians in a circle?

I'm thinking of a wheel of fortune type of thing where you have to check if a marker lands on a slot. Visually, we can see 0, 2pi, 4pi, etc... are in the same position. How do I check if 0 is equal to 2pi/4pi programmatically? Assuming I have the radius as well, I thought, maybe I have to convert it to cartesian coordinates first and then compare it. However, is there a better way to do this?

Edit: Also, I should make clear that the mark can land anywhere in between a slot. For example, the marker could be anywhere in between 0 to pi/6.

Upvotes: 0

Views: 309

Answers (1)

sabof
sabof

Reputation: 8192

Is this what you want?

var smallestEquivalentValueInRadians = originalValueInRadians % (2 * Math.PI);

If you want to compare, you can do:

a % (2 * Math.PI) === b % (2 * Math.PI)

% is the modulo operator, basically it subtracts the second operand from the first, as many times as it can (assuming you are dealing with positive numbers).

To cater for negative values:

function normalizeRadian(a) {
  var circle = Math.PI * 2;
  a = a % circle;
  if (a < 0) {
    a += circle;
  }
  return a;
}

Also when comparing floats, it's a good idea to have some "fuzzyness", since opperations on them can be imprecise.

function fuzzyEqual(a, b) {
  var fuzz = 0.001;
  return a < b + fuzz && a > b - fuzz;
}

So the complete solution is:

function fuzzyEqualRadians(a, b) {
  return fuzzyEqual(normalizeRadian(a), normalizeRadian(b));
}

Upvotes: 1

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