CODEWITHSUNDEEP
iphonemath
senthilmuthu
senthilmuthu

Reputation:

how to calculate inverse tan?

I am using UIAcceleration for rotation. I have opposite side, adjacent side, but I want to calculate tan-1(y/x) inverse tan.

Upvotes: 0

Views: 7664

Answers (3)

David Maymudes
David Maymudes

Reputation: 5654

atan2(y, x) is the same thing as atan(y/x), but it can deal properly with the case where x = 0 (i.e. a vertical line going up or down) without having do deal with positive vs. negative infinity.

Upvotes: 2

Louis Gerbarg
Louis Gerbarg

Reputation: 43452

The standard C math.h functions are available:

#include <math.h>

...
float theta = atan2f(y, x);
...

Upvotes: 4

Jason S
Jason S

Reputation: 189626

Always use atan2(y,x) instead of atan(y/x), for two reasons. One is mentioned by David Maymudes (problems with x=0). The other is that atan2() deals with the full range from -π to +π, whereas atan() only gives you an output between -π/2 and +π/2, and cannot distinguish between (x,y)=(2,2) and (x,y)=(-2,-2) since you lose the sign information when you do the division and pass only the quotient y/x into atan().

Upvotes: 8

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