SmartPoly is a mode that lets you draw a rectangular bounding box around the object that is automatically transformed into a polygon.
To use SmartPoly, select the Polygon label type from the Labels bar.
Click the icon on the label type to switch to SmartPoly mode. The icon will turn blue when SmartPoly is enabled.
For best results, zoom in first so you can draw a tighter rectangle around the object.
Select the location of your first corner and click and release, then drag the cross-hairs across the object so that the bounding box surrounds the object completely, and finally click and release at the opposite corner.
After a moment, the rectangular bounding box will turn into a polygon around the object.
SmartPoly works best when:
Object is against a contrasting background
Object is not overlapping with other objects
Bounding box is tight around the object