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Question by VillianT · Jan 20, 2012 at 03:08 AM · mathf

Mathf.Cos error

Why is that Mathf.cos is not accurate??
Here is my code:

function Update () { print(Mathf.Cos(135)); }

unity will print -0.9960 but is should be -0.7071?!
I try it on my calculator?
Is this a bug?
by the way I'm using unity 3.4.0f5

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Answer by syclamoth · Jan 20, 2012 at 03:33 AM

Mathf.Cos uses radians, not degrees. Try

 Mathf.Cos(135 * Mathf.Deg2Rad);

and see what you get!

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avatar image Bunny83 · Jan 20, 2012 at 04:00 AM 1
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jep, 135 modulo PI is 3.053...
converted to degree:
174.93...
cos(174,93...) = -0.9960...

Usually in most program$$anonymous$$g languages the trigonometric functions work with radians.

avatar image VillianT · Jan 20, 2012 at 04:11 AM 0
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@syclamoth wow thank you very much now I get the right answer! I didn't know that $$anonymous$$athf.Cos uses radians, not degrees. I thought it is just the same as my calculator... lol

avatar image syclamoth · Jan 20, 2012 at 04:16 AM 0
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Your calculator probably uses radians, too- you just don't notice because it defaults to degrees!

avatar image panta · Jun 01, 2013 at 10:13 PM 0
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Wow, thanks very much for pointing this out. I love Unity and I'd never switch engines, but man is the documentation incomplete. For $$anonymous$$athf.Cos, it reads: "static function Cos (f : float) : float Description

Returns the cosine of angle f in radians."

Nowhere does it specify that parameter "f" must be in radians - it just says the return type is radians! You basically just have to try them both and realize the values are bogus if you input degrees.

avatar image syclamoth · Jun 03, 2013 at 03:29 AM 1
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Haha, the return value isn't in radians, since that doesn't even make sense. Sine and Cosine do not return angles, they return a value between -1 and 1, so the only thing that the radians could be referring to is the input.

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