I did some comparisons between the Rhino 7 WIP loft subD option and the subD loft command in a plug-in I’ve used for a while. Detailed analysis below, and here’s the file: Lofting.3dm (221.2 KB)
1. Lofting open degree 1 curves.
Below are four different results of lofting the same degree 1 curves. Rhino 7 WIP is in blue. A third party plugin is in red. Source curves are behind them, with one pair rebuilt with extra edit points.
Far left: WIP, simple source curves, “rebuild with 7 control points” selected in options
Near left: WIP, source curves rebuilt with 7 control points, “do not simplify” selected in options
Near right: Plugin. Options = 3 segments, 1 “along” segment
Far right: Plugin. Options = 3 segments, 3 “along” segments
The key differences here seems to be that the plugin detects discontinuities, and somehow figures out how to treat them as separate segments even when only one source polyline has a discontinuity. It also allows for “along” segments.
Also: Rhino defaults to crease the outermost vertices. Plugin defaults to not. Should there be an option?
The plugin seems to do better than what the WIP can do right now. I would think a typical user would expect output that looks more like the plugin.
I realize lofting polylines may seem like a special case, but one of the greatest things about SubD is that it can take complex planar faced polysurfaces and make it much easier to soften/blend their edges that is possible in NURBS. So this may be more of a key feature than it seems.
OK, now for where the Rhino 7 WIP beats the plugin, mostly…
2. Lofting Closed Degree 3 Curves
Again, below are different results from lofting the same curves. Rhino in blue, plugin Red. Source curves shown with _EditPtOn for clarity.
Far Left: Rhino 7 WIP, “Do not Simplify” option checked.
Near left: Plugin, options = 8 segments, 2 “along” segments
Near right: Plugin, options = 8 segments, 4 “along” segments
Far right: Rhino 7 WIP, “Do not simplify” option checked, and then _InsertEdge run, with “both sides”, proportional options, 0.5 entered.
Rhino’s choice to line up subD edges with input curve knots is clearly superior. The plugin just divides the curves into equal segments, and thus it requires many more subdivisions to get equivalent detail.
However: the option to have “along” segments within the command is still better. The furthest right example simulates the best of both worlds. Again, one of the looks users go for when using SubD is linear, but smoothed. In this example, it’s easy to achieve quickly with a second command, but with more complex examples, including “along” segments would make workflow faster. Same goes for any future SubD-capable grasshopper loft component.
3. Creases at seams? Is this a bug?
Using the “rebuild with X control points” option with a subD loft apparently produces a crease wherever the user places the loft’s seam.
- Feature or bug? Should there be a “crease seam” checkbox or just no crease?
- Is the “rebuild” option meant to be used with SubD’s at all?
- Also: in some cases, when trying to use an intentional twist in the seam to create a warp in the loft, I got no output at all.
- There is another bug where sometimes the number of control points to rebuild by gets “stuck” and applies itself even when the user clicks back to “do not simplify”. Tried exiting and rerunning the command to get around it and it still happened. Can’t figure out what conditions create this problem though.
Did anyone read this whole thing? THANK YOU.
