Order them counter-clockwise. For consistency with the default, start at the upper left corner. The upper left corner for a horizontal surface is underdefined.

corner.

The Online help for GlobalGeometry Rules tells us that the shadowing algorithms require the vertices 'in a certain order and positional structure' and goes on to say Surfaces are always 'viewed from the outside of the zone'

The Engineering Reference includes the key detail: 'listed counter-clockwise'. All of this can be summarised as 'use the right hand rule'. There is some missing info for horizontal surfaces.

Order them counter-clockwise. For consistency with the default, start at the upper left corner.

The Online help for GlobalGeometry Rules tells us that the shadowing algorithms algirthms require the vertices 'in a certain order and positional structure' and goes on to say Surfaces are always 'viewed from the outside of the zone'

The Engineering Reference includes the key detail: 'listed counter-clockwise'. All of this can be summarised as 'use the right hand rule'.