Question:
What is the easiest way to define a polygonal surface graphically?
Answer:
Basically, there are two options:
If no structural lines are defined yet, a polygonal surface can be defined by menu bar → "Insert" → "Model Data" → "Surfaces" → "Plane" → "Graphically" → "Polygon", see picture 1
If structural lines are already defined, a polygonal surface can be defined by menu bar → "Insert" → "Model Data" → "Surfaces" → "Plane" → "Graphically" → "Select Boundary Lines", see picture 2