How to Calculate Centroid

Question

I am working with geospatial shapes and looking at the centroid algorithm here,

http://en.wikipedia.org/wiki/Centroid#Centroid_of_polygon

I have implemented the

Answer 1

For 3d Points, I created a method in C # I hope I can help you:

public static double[] GetCentroid(List<double[]> listOfPoints)
    {
        // centroid[0] = X
        // centroid[1] = Y
        // centroid[2] = Z
        double[] centroid = new double[3];

        // List iteration
        // Link reference:
        // https://en.wikipedia.org/wiki/Centroid
        foreach (double[] point in listOfPoints)
        {
            centroid[0] += point[0];
            centroid[1] += point[1];
            centroid[2] += point[2];
        }

        centroid[0] /= listOfPoints.Count;
        centroid[1] /= listOfPoints.Count;
        centroid[2] /= listOfPoints.Count;

        return centroid;
    }

Answer 2

This answer is inspired by the answer by Jer2654 and this source: http://coding-experiments.blogspot.com/2009/09/xna-quest-for-centroid-of-polygon.html

  /// <summary>
  /// Method to compute the centroid of a polygon. This does NOT work for a complex polygon.
  /// </summary>
  /// <param name="poly">points that define the polygon</param>
  /// <returns>centroid point, or PointF.Empty if something wrong</returns>
  public static PointF GetCentroid(List<PointF> poly)
  {
     float accumulatedArea = 0.0f;
     float centerX = 0.0f;
     float centerY = 0.0f;

     for (int i = 0, j = poly.Count - 1; i < poly.Count; j = i++)
     {
        float temp = poly[i].X * poly[j].Y - poly[j].X * poly[i].Y;
        accumulatedArea += temp;
        centerX += (poly[i].X + poly[j].X) * temp;
        centerY += (poly[i].Y + poly[j].Y) * temp;
     }

     if (Math.Abs(accumulatedArea) < 1E-7f)
        return PointF.Empty;  // Avoid division by zero

     accumulatedArea *= 3f;
     return new PointF(centerX / accumulatedArea, centerY / accumulatedArea);
  }

Answer 3

public static Point GetCentroid( Point[ ] nodes, int count )
{
    int x = 0, y = 0, area = 0, k;
    Point a, b = nodes[ count - 1 ];

    for( int i = 0; i < count; i++ )
    {
        a = nodes[ i ];

        k = a.Y * b.X - a.X * b.Y;
        area += k;
        x += ( a.X + b.X ) * k;
        y += ( a.Y + b.Y ) * k;

        b = a;
    }
    area *= 3;

    return ( area == 0 ) ? Point.Empty : new Point( x /= area, y /= area );
}

Answer 4

You may check if .NET 4.5 DbSpatialServices functions, like DbSpatialServices.GetCentroid