How do Apostle's get called?

We are so blessed to have a living prophet and apostles who lead us in righteousness during these days. They are a mouthpiece of our Savior on the earth. They counsel and let us know what it is that Christ would have us do. We love them and their dedication to serve. Within just the past six month three of our dear apostles have left us on this earth; President Packer, Elder Perry, and Elder Scott. With their passing will come the call to 3 new apostles. How is that call made? Here is a great article explaining the process of Calling and Apostle of God.