How are IOUs for ground truth boxes in YOLO calculated?

I know how IOU works during detection. However, while preparing targets from ground-truth for training, how is the IOU between a given object and all anchor boxes calculated?

Is the ground truth bounding box aligned with an anchor box such that they share the same center? (width/2, height/2)

I think this is the case but I want to hear from someone who has better knowledge of how training data is prepared for training in YOLO.