public Vector3f getCenter() {
        if (center == null) {
            calculateCenter();
        }
        return center;
    }
Accesses the stored centroid (the average of the 3 vertex locations)
calculating it if it is null.

@return the coordinates of the center (an internal vector subject to
re-use)
jme3-core/src/main/java/com/jme3/math/Triangle.java