Produce a rectangle with rounded corners. The optional argument portion allows you to produce only half or a quarter of the oval. For half an oval take portion to be one of these.
Produce only one quarter of the oval by setting portion to
This draws the top half of an oval that is 3 wide and 7 tall.
The (5,7) is the center of the entire oval, not just the center of the top half.
These shapes are not ellipses. They are rectangles whose corners are made with quarter circles. These circles have a maximum radius of 20pt (see \circle for the sizes). Thus large ovals are just boxes with a small amount of corner rounding.