planefit PolygonArea

import Rhino
import clr
clr.AddReferenceToFile("KangarooSolver.dll")
import KangarooSolver as ks
from System import Array, Double, MissingMemberException

class PolygonArea(ks.GoalObject):
    def __init__(self, P, area, strength=1):
        try: # convert polylinecurve
            _,P = P.TryGetPolyline()
        except MissingMemberException:
            pass
        self.PPos = Array[Rhino.Geometry.Point3d](P)
        self.Move = Array.CreateInstance(Rhino.Geometry.Vector3d, len(self.PPos))
        self.Weighting = Array[Double]([strength] * len(self.PPos))
        self.Strength = strength
        self.TargetArea = area

    def Calculate(self, p):
        Array.Clear(self.Move, 0, self.Move.Length)
        Array.Clear(self.Weighting, 0, self.Weighting.Length)

        xfpts = [Rhino.Geometry.Point3d(p[self.PIndex[i]].Position) for i in range(self.PIndex.Length)]
        pfresult, plane = Rhino.Geometry.Plane.FitPlaneToPoints(xfpts)
        if pfresult == Rhino.Geometry.PlaneFitResult.Failure:
            raise RuntimeError("Couldn't fit plane to points")

        # keep stable plane orientation
        if plane.Normal.CompareTo(Rhino.Geometry.Plane.WorldXY.Normal) == -1:
            plane.Flip()
        plane = Rhino.Geometry.Plane(Rhino.Geometry.Point3d.Origin, plane.Normal)

        xform = Rhino.Geometry.Transform.ChangeBasis(Rhino.Geometry.Plane.WorldXY, plane)
        for pt in xfpts:
            pt.Transform(xform)

        areadoubled = 0
        totallength = 0
        L = self.PIndex.Length
        for i in range(L):
            p1, p2 = xfpts[i], xfpts[(i+1)%L]
            areadoubled += Rhino.Geometry.Vector3d.CrossProduct(
                Rhino.Geometry.Vector3d(p1),
                Rhino.Geometry.Vector3d(p2)).Z
            totallength += p1.DistanceTo(p2)
        areashortage = self.TargetArea - 0.5 * areadoubled
        offset = areashortage / totallength

        for i in range(L):
            nexti = (i+1) % L
            edge = p[self.PIndex[nexti]].Position - p[self.PIndex[i]].Position
            edge.Unitize()
            pressure = offset * Rhino.Geometry.Vector3d.CrossProduct(edge, plane.ZAxis)
            self.Move[i] += pressure
            self.Move[nexti] += pressure
            self.Weighting[i] = self.Strength