What command to improve these profiles for a sweep?


I have used extractIsocurves to get these profiles for the side of an aircraft cowling, drawn in my early days, to attempt to tidy up the surface before smash. The existing cowling created a smash shape not befitting the source as I had hoped.

as they feature an untidy array of points, they need redrawing with a limit set to so many points. I recall profiles are best with the same number of points, I cannot remember the command to do so.

The kink at ‘A’ is correct , it becomes none over a distance of 100mm or so heading across the panel left to right, but not that at B, that one can flow better.

I also wonder if its best to sweep left to right or top to bott due to the S curve at top. The hole doesnt matter, I can do away with it.

see attached…
refine cowling for smash.3dm (311.5 KB)


This is true in some cases and not in others - surfacing commands that do not use the input curve structure, like NetworkSrf, do not care. But, I think what you are looking for is Rebuild.


Hi Pascal,
ah yes Rebuild. used it on first curve with ‘A’ at top and it lost me the kink, oh :frowning:

When making aircraft wings I used rebuild for all the profiles as that was correct method for such.

Googling this I see someone saying FitCrv.

Tried for FitCrv and it retained the kink, so maybe FitCrv on that one and rebuild on others.

I am sure though that FitCrv could do better on that S curve, doesnt take that many points to draw that, and could give less points along that entire line. Rebuild just killed it.

If I am to reskin using these, I was going for Sweep 2rail with top and bott as rails, would NetworkSrf then be better ? I was worried what that S bend in rail might do and oddments such as that can cause hrs of work solving it.
trying both NetworkSrf and sweep2rail that S curve us causing an issue in what should be a smooth surface, I am getting a myriad of lines as well when this surface should see a few.

attached how it is without the S bend being used. Not sure how to stop the S curve causing upset to what should be a smooth surface.
refine cowling for smash.3dm (430.2 KB)

I have tried three separate ways of skinning that apparent simple shape, and all of them produce rubbish smashes.

refine cowling for smash 3 attempts.3dm (1.4 MB)


you should make your boundary curves cleaner and then retrim, to create a simpler surface like this:

simple-surface.3dm (346.2 KB)

that sure makes a simpler panel, mine was done in the early days of learning rhino, and its with smash as hoped for, comparing your profiles featuring just a few control points to those of mine after treating them to rebuild 10 points, I see the attached file differences.
You do however lose an intended kink at ‘A’ that is there on the real thing and that feathers out over 100mm or so.
The S curve caused me great problems in its effect on the sweep. I feel mention of trim solves that if you can explain how you do that. Such required shapes give me grief on sweeps etc.

Orange hatch where shrinkage inwards occurs and black for expansion outwards.
The widest hatches are:-
shrinkage of 6.5mm (orange) and gain of 2.9mm (black)

I would have to revisit my cowling plans and data to see if this was a more accurate rendition of the cowling or if it changed from the true shape. as those are quite significant distances.

I need to know though as this is most effective how did you do that please. Especially you say retrim, I am not familiar with that at all and see the control point lines beyond the skin.
I could then redo my earlier work which was a real mix of isocurves like a patchwork quilt !

simple-surface analyse difference.3dm (603.1 KB)
I see my hatches ended up on one plane yet I didnt have project to cplane on, no time to move them though.


I did not look into replicating your surfaces accurately but rather wanted to point out that a surface with less control points is a lot easier to handle and manipulate.
With retrim I simply mean to have the boundary of your original surfaces as reference and once the clean surfaces are built and are within tolerance of your original surfaces, use those to trim the simple surface.
As for the kink: I did not know it was intentional, thought it was a kink due to the way the surfaces were constructed.

Better to split that curve at the kink and treat as 2 curves, rejoin later…

Rather than using the top edge to form a surface, it may be better to use is as a trimmer once you have a nice surface lofted from the rebuilt curves. Here is a short video to demonstrate a method.

For Steve V5.3dm (332.1 KB)