Specific area under curve

I have two sets of data - pressure and volume. Plotting volume on the x axis and pressure on the y axis, the plot is obtained as shown in the figures. Some plots will have loops (marked in red, highlighted in yellow). I want to know if there is any way to determine the presence of those smaller (inner) loops or area under those smaller (inner) loops.

(with small inner loops)

(without any inner loop)

Answer 1

[Benjamin Thompson]

You could locate the "center" of the large circle or oval. Try calculating the polar cordinates, angle and radius, from the center to each data point. Any angle used more than once, or if the rate of change in angle backtracks, is a likely place for an inner loop.