Outline Lines are independent straight-line segments defined by two points. They are distinct from regular PhotoModeler lines connecting two points. They are used to define a straight edge of a shape. When drawing an Outline Line, click the first point of the line - a menu of surface IDs will pop up and allow you to select the associated surface that it needs (if Shift not held). You then move the cursor to the end of the line or edge and complete by clicking again.
A new Line can be drawn either on its own, or by clicking on and using the end point of a different object. Outline Lines can also be connected to other Outline entities via a fillet (see Fillet Tools).
At any time in this mode, an existing Outline point can be clicked and dragged to adjust its photo position.
A concept for drawing Outline Lines on something like a rectangle with rounded corners, is the four lines are drawn so they do not connect at the corners. Their ends fall short of the corners or even short of where the rounded part starts. Filleting is then used to join the lines and form the rounded corners. The Line ends will modify as needed.