Having trouble figuring out how to specify the offset to go outwards in all directions. Any suggustions?
specifically offsetting the polylines that stretch across horizontally*
The offset of what? The points? The curves (which could be re-derived from the points)? The surface from lofting the arcs? Oh, I see that Loft resulted in four joined surfaces… That complicates things.
Oh, I used interpolated curves instead of polylines but you can have polylines instead (disabled):
data tree arch_2020Sep5aa.gh (19.8 KB)
(re-posted to correct error)
Thank you for showing me three different ways to do that replies like this really help me learn and i appreciate it
The different methods have trade-offs. The offset points and curves from Offset Surface don’t touch the ground. The Vector 2Pt method is better when the Z value for the center point of the arcs is close to their distance from the guide curves (10), but not as good when that value is lower (3, for example). Yet another method would be Scale but the results are similar, depending on what you use for its ‘C’ (Center) input.
Maybe the best method would be to offset the two guide curves and build arches from those? I managed to do that by clustering the code… Rats! It looks exactly the same as version ‘c’. 
data tree arch_2020Sep6a.gh (34.5 KB)
Inside the cluster:
