To Place an Ellipse by Center and Edge

Select the Place Ellipse tool (Drawing > Home > Placement > Ellipse Tools split button ).
In the tool settings window, set Method to Center.
Enter a data point to define the center.
If Primary, Secondary, and Rotation are on, the ellipse is placed.

If necessary, enter a data point.

Constraints on	Data point defines the following
None	Ellipse rotation and primary axis radius.
Rotation	Primary axis radius.
Primary	Secondary axis radius.

If necessary, enter a third data point.
If Secondary is off, it defines the secondary axis radius.

Right: Place Ellipse, with Method set to Center and all constraints off. Left: Place Ellipse, with Method set to Center and all constraints on. Primary axis denoted by P. Secondary axis denoted by S. Rotation angle denoted by A.