Thank you for your detailed request. The problem of capping a dome-like structure is indeed tricky. To do it through Xirus I suggest using the Match&Blend commands. XirusPatch will not work here because the input lines are too smooth (XirusPatch requires a polygonal input to give good results).
In general I recommend two ways of tackling it:
1- Using Rhino Patch command.
Just run Rhino command Patch over the input curves. You’ll get something like this:
2- Using Xirus Match&Blend commands.
First step is to join the surface patches containing the input boundary curves of the dome, by selecting them and running XirusJoin.
Second step is adding a Xirus primitive that will be the dome roof itself: for example I added a Xirus disk (command XirusSurfacesDisk) with 3 U Points and 2 V Points. I transformed and placed it at a proper height with respect to the shape curves. It’s also possible to tweak its surface points and derivatives at this point.
Third step is running command XirusWatertightBlendEdgeLoops to blend the dome upper edge loop with the disk lower edge loop. I got this surface:
The alternative with Xirus is slightly more complex than that of Rhino Patch, but in return there’s more possibilities to create different designs and transitions between primitives.
Also, we just updated XirusCAD to version 18.104.22.168., which fixes some glitches related to Match&Blend commands.