I have some acceleration values from a sensor. These values are reported as x, y and z components of the acceleration. As can be seen in the attached figure, it is clear that the z signal has a clear sinusoidal curve present. Is there any algorithm to quantify the "sinusoidalness" of a curve. I am trying to write an algorithm that would identify the z signal of the attached image to be the most sinusoidal.
Edit: The variation could indeed be greater in any of the axes without the most sinusoidal signal. The original problem being solved here is to count the number of breaths in the accelerometer signal. To do this first the axis containing the breathing signal must be identified. From the image it is obvious that for the first image the z-axis has the breathing data and for the second image the x-axis has the breathing data