Create Cubic Bezier Curves

Hi,

 

 

I have to transform a series of points to a line consisting of cubic Bezier curves. I couldn't find a function to do that in existing transformers or the Python API of FME Objects. The Generalizer (NURBfit algotirhm) creates a spline curve, but it's not exact cubic Bezier curves. The expected line has to pass through the both ends of each 3 segments.

 

  So, I wrote the following script. Is this the "re-invention of the wheel"? If you know an existing function (transformer or Python function) that creates cubic Bezier curves based on control points, please let me know. 

 

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import fmeobjects   class CubicBezierCurveReplacer(object):     def __init__(self):         self.set_coefficients(32)              def set_coefficients(self, n):         self.n = n         r = 1.0 / float(self.n)         s = range(0, self.n)         self.k0 = [(1.0 - (r * m))**3 for m in s]         self.k1 = [3.0 * (r * m) * (1.0 - r * m)**2 for m in s]         self.k2 = [3.0 * (1.0 - (r * m)) * (r * m)**2 for m in s]         self.k3 = [(r * m)**3 for m in s]              def bezier_coords(self, p):         coords = []         x0, x1, x2, x3 = p[0][0], p[1][0], p[2][0], p[3][0]         y0, y1, y2, y3 = p[0][1], p[1][1], p[2][1], p[3][1]         for i in range(1, self.n):             x = self.k0[i] * x0 + self.k1[i] * x1 + self.k2[i] * x2 + self.k3[i] * x3             y = self.k0[i] * y0 + self.k1[i] * y1 + self.k2[i] * y2 + self.k3[i] * y3             coords.append((x, y))         return coords              def input(self, feature):         # If the number of coordinates is less than 2, return nothing.         if feature.numCoords() < 2: return                  # Get all coordinates of the input feature as control points.         points = feature.getAllCoordinates()                  # Append coordinates while (number of control points - 1)         # is not divisible by 3 evenly.         while (len(points) - 1) % 3 != 0:             points.append(points[-1])                      # Create  cubic Bezier curves.         bezier = feature.cloneAttributes();         bezier.setGeometryType(fmeobjects.FME_GEOM_LINE)         bezier.setCoordSys(feature.getCoordSys())         bezier.addCoordinate(points[0][0], points[0][1])         for i in range(3, len(points), 3):             bezier.addCoordinates(self.bezier_coords(points[i - 3 : i + 1]))             bezier.addCoordinate(points[i][0], points[i][1])         self.pyoutput(bezier)              def close(self):         pass -----

 

 

Takashi