ODTK Rotated Bounding Box Label Format

I am trying to develop a rotated bounding box model for my custom dataset and have followed:

In the blog it says "Now you can describe the bounding box of an object using xmin, ymin, width, height and θ. "
And on the odtk github page it says: “bbox” : [x, y, w, h, theta]

So my question is should x and y be the center of the rotated box or xmin and ymin? And if the latter should xmin and ymin be the absolute minimum x and y values or coordinates from the same corner?

rotated rectangle

Should the x and y values for the example above be:

  1. x1, y1
  2. x4, y1
  3. centre x, centre y

I assume option 1 is the correct answer but confirmation of this would be good as I cannot seem to find a concrete answer.