How to get normals of a 2D line and to integrate along it

ParaView Support
5

Dear @Kenneth_Moreland ,
thanks a lot for taking the time to write such a didactic and complete answer.
But if I may ask, what are criteria for return cell end points with GetPointId?
For I can think of such a solution

 for i in range(numCells):
  cell = input0.GetCell(i)
  p1 = input0.GetPoint(cell.GetPointId(0))
  p2 = input0.GetPoint(cell.GetPointId(1))
  dx= p2[0] - p1[0]
  dy= p2[1] - p1[1]
  normx[i] = dx
  normy[i] = dy

But if the grid is unstructured how can I be sure, traversing the airfoils’s wall in the for cycle, to get p1(i), p2(i) and p1(i+1) and p2(i+1) to be the ordered points that I would got traversing the airfoil’s wall in a choerent clockwise or counter-clockwise manner ?
Again, thank you for your answer.