Untitled

 public static Point3d PolylineCentroid(ZwSoft.ZwCAD.DatabaseServices.Polyline polyline)
        {
            double area = 0;
            double cx = 0;
            double cy = 0;
            int numVertices = polyline.NumberOfVertices;
            for (int i = 0; i < numVertices; i++)
            {
                Point2d p1 = polyline.GetPoint2dAt(i);
                Point2d p2 = polyline.GetPoint2dAt((i + 1) % numVertices);

                // Determinante para cálculo da área e dos centroides
                double determinant = (p1.X * p2.Y) - (p2.X * p1.Y);
                area += determinant;
                cx += (p1.X + p2.X) * determinant;
                cy += (p1.Y + p2.Y) * determinant;
            }
            area *= 0.5;
            cx = (cx / (6 * area));
            cy = (cy / (6 * area));
            return new Point3d(cx, cy, 0);
        }