12. The method of claim 11 further comprising the step of counting the number of the trough coordinates.
11. The method of claim 1 , wherein step (e) includes the steps of: computing an average and a standard deviation by computing the average and the standard deviation of those vertical projections being greater than 0, respectively; computing a second threshold being the average subtracted by a second threshold coefficient multiplying the standard deviation; selecting at least one trough coordinate, the vertical projection of which is smaller than the second threshold; and selecting the third coordinate from the trough coordinates.