private static float calcScreenArea(BoundingSphere bound, float distance, float screenWidth) {
        // Where is the center point and a radius point that lies in a plan parallel to the view plane?
        //    // Calc radius based on these two points and plug into circle area formula.
        //    Vector2f centerSP = null;
        //    Vector2f outerSP = null;
        //    float radiusSq = centerSP.subtract(outerSP).lengthSquared();
        float radius = (bound.getRadius() * screenWidth) / (distance * 2);
        return radius * radius * FastMath.PI;
    }
Estimate the screen area of a bounding volume. If the volume isn't a
BoundingSphere, BoundingBox, or OrientedBoundingBox, 0 is returned.

@param bound The bounds to calculate the volume from.
@param distance The distance from camera to object.
@param screenWidth The width of the screen.
@return The area in pixels on the screen of the bounding volume.
jme3-core/src/main/java/com/jme3/util/AreaUtils.java