STAR-CCM+ uses a point on a part to rotate. If you select a point somewhere other than on a part, STAR-CCM+ uses the depth to that last point; the depth is normal to the view plane.
The scene can be rotated around various axes, depending on the direction you move the mouse.
Choose a point on or near the object in the visualization display, and click and drag (holding down the left mouse button) in a horizontal direction from that point.

This action rotates the object around the vertical axis. The small colored square represents the point at which you began the click-and-drag motion. The colored number near it indicates degrees of rotation.
Now try clicking and dragging in a vertical direction.

The axis is horizontal.
Click and drag at an angle.

The two directions of the axes are combined.
This technique rotates the object around the axis perpendicular to the direction of your drag. You set the location of the axis when you chose a point to begin clicking and dragging.