In Image segmentation, there is a method named 'Active Contour model' which is used to segment deformable model.In 'Active contour model', there are some techniques where the relation of a particular point is found out and it is multiplied by outward unit normal vector of a curve.

What is the best way to find that?or Do the geometrical method like finding tangent and then normal is to be used?

Is there any relation of outward unit normal vector with Signed distance map?