Find the center of a face

Developers Ruby API
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17

I added your suggestion to get this (finally):

  def get_centroid(pts)
    total_area = 0
    total_centroids = Geom::Vector3d.new(0,0,0)
    third = Geom::Transformation.scaling(1.0 / 3.0)
    npts = pts.length
    vec1 = Geom::Vector3d.new(pts[1].x - pts[0].x, pts[1].y - pts[0].y, pts[1].z - pts[0].z)
    vec2 = Geom::Vector3d.new(pts[2].x - pts[0].x, pts[2].y - pts[0].y, pts[2].z - pts[0].z)
    ref_sense = vec1.cross vec2
    for i in 0...(npts-2)
      vec1 = Geom::Vector3d.new(pts[i+1].x - pts[0].x, pts[i+1].y - pts[0].y, pts[i+1].z - pts[0].z)
      vec2 = Geom::Vector3d.new(pts[i+2].x - pts[0].x, pts[i+2].y - pts[0].y, pts[i+2].z - pts[0].z)
      vec = vec1.cross vec2
      area = vec.length / 2.0
      if(ref_sense.dot(vec) < 0)
         area *= -1.0
      end
      total_area += area
      centroid = (vec1 + vec2).transform(third)
      t = Geom::Transformation.scaling(area)
      total_centroids += centroid.transform(t)
    end
    c = Geom::Transformation.scaling(1.0 / total_area)
    total_centroids.transform!(c) + Geom::Vector3d.new(pts[0].x,pts[0].y,pts[0].z)
  end

This should work for convex and concave polygons.

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