3d Accelerometer calculate the orientation

Question

I have accelerometer values for the 3 axes (usually when there is only gravity contains data between -1.0 and 1.0 ):

  float Rx;
  float Ry;
  float Rz;
         


        

Answer 1

I've tried the recommended solution (matteo's), and while it seemed to work great at first, I noticed that when the pitch approaches 90 degrees (starting at around 70 degrees but not necessarily consistent across different phones), the roll suddenly surges. When the pitch is at 90 the roll that should be around 0 is now at over 100 and keeps increasing to 180. I'm trying to think of a way to mathematically prevent this, if I restrict the roll to +90/-90 it behaves normally but I don't get the range I want (+180/-180): Math.atan2(y, Math.sqrt((xx) + (zz))) * (180/Math.PI))