I have a closed convex polyhedron which is defined by an array of convex polygons (faces) which are defined by arrays of vertices in 3D space. I'm trying to find the centroid of the polyhedron, assuming uniform density. At the moment I calculate it with the algorithm in this pseudo-code.

```
public Vector3 getCentroid() {
    Vector3 centroid = (0, 0, 0);
    for (face in faces) {
        Vector3 point = face.centroid;
        point.multiply(face.area());
        centroid.add(point);
    }
    centroid.divide(faces.size());
    return centroid;
}

```

This essentially takes the weighted average of the centroids of the faces. I'm not 100% sure this is correct as I haven't been able to find a correct algorithm online. If someone could either confirm my algorithm or refer me to a correct one I would appreciate it.

Thanks.

---

[EDIT]

So here is the actual Java code I am using to find the centroid. It breaks the polyhedron into pyramids converging on an arbitrary point inside the polyhedron. The weighted average for the pyramid centroids is based on the following formula.

Call = SUMall pyramids(Cpyramid \* volumepyramid) / volumeall

Here is the (*heavily* commented code):

```
    // Compute the average of the facial centroids.
    // This gives an arbitrary point inside the polyhedron.
    Vector3 avgPoint = new Vector3(0, 0, 0);
    for (int i = 0; i < faces.size(); i++) {
        avgPoint.add(faces.get(i).centroid);
    }
    avgPoint.divide(faces.size());

    // Initialise the centroid and the volume.
    centroid = new Vector3(0, 0, 0);
    volume = 0;

    // Loop through each face.
    for (int i = 0; i < faces.size(); i++) {
        Face face = faces.get(i);

        // Find a vector from avgPoint to the centroid of the face.
        Vector3 avgToCentroid = face.centroid.clone();
        avgToCentroid.sub(avgPoint);

        // Gives the unsigned minimum distance between the face and a parallel plane on avgPoint.
        float distance = avgToCentroid.scalarProjection(face.getNormal());

        // Finds the volume of the pyramid using V = 1/3 * B * h
        // where:   B = area of the pyramid base.
        //          h = pyramid height.
        float pyramidVolume = face.getArea() * distance / 3;

        // Centroid of a pyramid is 1/4 of the height up from the base.
        // Using 3/4 here because vector is travelling 'down' the pyramid.
        avgToCentroid.multiply(0.75f);
        avgToCentroid.add(avgPoint);
        // avgToCentroid is now the centroid of the pyramid.

        // Weight it by the volume of the pyramid.
        avgToCentroid.multiply(pyramidVolume);

        volume += pyramidVolume;
    }

    // Average the weighted sum of pyramid centroids.
    centroid.divide(volume);

```

Please feel free to ask me any questions you may have about it or point out any errors you see.