title: How to insure spline goes through points
body: <p>I am trying to make a spline to compute the derivative of a <a href="https://stackoverflow.com/questions/31331874/exemplar-based-inpainting-how-to-compute-the-normal-to-the-contour-and-the-iso">contour</a> of a part of an image. The catch is that I don't seem to know how to make the spline go through a certain point. I am using the scipy.interpolate library with the UnivariateSpline method. </p>