RuntimeWarning invalid value encountered in sqrt distance = focal_length npsqrtactual_area npsqrtpixel_area

This warning occurs when the code encounters a negative or complex number while trying to calculate the square root. This usually happens when the input values are not valid or the calculations involve complex numbers.

To fix this, you can check the input values and make sure they are within the expected range. You can also handle complex numbers by using the complex square root function (cmath.sqrt) instead of the regular square root function (math.sqrt).