How to swap negative rotation values over to positive rotation values?

Question

Example: I have a circle which is split up into two halfs. One half goes from 0 to -179,99999999999 while the other goes from 0 to 179,99999999999. Typical example: transform.rotation.z of an CALayer. Instead of reaching from 0 to 360 it is slip up like that.

So when I want to develop a gauge for example (in theory), I want to read values from 0 to 360 rather than getting a -142 and thinking about what that might be on that 0-360 scale.

How to convert this mathematically correctly? Sine? Cosine? Is there anything useful for this?

Answer 1

Isn't the normalization achieved by something as simple as:

assert(value >= -180.0 && value <= +180.0);
if (value < 0)
    value += 360.0;

I'd probably put even this into a function if I'm going to need it in more than one place. If the code needs to deal with numbers that might already be normalized, then you change the assertion. If it needs to deal with numbers outside the range -180..+360, then you have more work to do (adding or subtracting appropriate multiples of 360).

Answer 2

Say x is the value with range (-180, 180), y is the value you want display,

  y = x + 180;

That will change shift reading to range (0, 360).

Answer 3

while (x < 0)  {
  x = x + 360;
  }

while (x > 360) {
  x = x - 360;
  }

This will work on any value, positve or negative.

Answer 4

If you don't mind spending a few extra CPU cycles on values that are already positive, this should work on any value -360 < x < 360:

x = (x + 360) % 360;

Answer 5

I provide code to return 0 - 360 degree angle values from the layer's transform property in this answer to your previous question.