Surface Creation: Splitting at tangents


I’ve been having repeated issues with Sweep2 not splitting at tangents while other similar commands do it with ease (sometimes I need to check a box). Is there a reason on why Sweep2 does not create a polysurface in the attached example?

TangentSplit.3dm (178.7 KB)

(Pascal Golay) #2

Hi Andrew - Yeah… it is a little weird - for the Extrude commands, you need to be making Breps (polysurfaces) and not Extrusion objects (UseExtrusions command) for this to work ‘right’…



Setting UseExtrusions to Polysurface did not do the trick with Sweep2 - It still creates one surface while the others create a polysurface composed of 2 surfaces (just like my previous example). Is it possible to split that surface while Sweep2 is making it or do I need to do it post creation? Either way is fine with me, it just strikes me as odd that 3 other commands generate a polysurface and one generates a surface

Edit: I have CreaseSplitting set to Yes

(Pascal Golay) #4

Ah, OK , right - Sweep2 does not split at tangents - no setting for that - I see that Sweep1 does split, because the default behavior is not to refit the rails, whereas Sweep2 does refit the rails. My guess is that Sweep1 can make simpler objects that reflect the curve structure better simply because it does not have to contend with another rail - it is rare that they are the exact same like this in Sweep2, usually the surface must be cooked up with different inputs on each side. If SimpleSweep is not available or not used in Sweep2, then the rails are refit to G2 across G1 joins, I believe.

CreaseSplitting should in general always be set to Yes - it ensures, if it’s working, that surfaces with actual creases (G0) are split up. It does not split ‘potential’ creases however. In Sweep2, if you use SimpleSweep, the rails are not refit and you can DivideAlongCreases the result. CreaseSplitting determines whether surfaces created behind the scenes are sent through the ‘kink splitter’ to be made into polysurfaces before being added to the document - it has no provision that I know of for dealing with G1 continuity, only actual kinks.



Hi Pascal,

Thanks for the explanation! Im looking into ways to improve the modeling output to generate toolpaths faster for our router and a big issue that keeps coming up is splitting a swept surface up by its tangent. I didnt realize simple sweep would actually help my issue; I assumed it rebuilt the curves prior to running the sweep and thus generate a single curve which would not allow for the sweep result to be broken up by DivideAlongCreases

(Joaquin Laborda) #6

Hi Pascal, thanks for the tips, I didn’t know about DivideAlongCreases, I can imagine 1000 cases where I would have used it in the past…
Immediately after that I though about a similar command but to do the opposite. Sometimes I receive files from other programs and all the surfaces come divided although they share the same structure and could be merged without problems one by one.
So my question is if there is a multiple merge command.

(Pascal Golay) #7

Hi Joaquin - there is only MergeSrf currently - one pair of surfaces at a time… I can imagine it would not be too hard and probably accurate enough to create a Network surface from curves extracted from these though. maybe?


(Joaquin Laborda) #8

Thanks Pascal, yes, depending on the case I merge the surface and use rebuild, or directly take some curves and create new surfaces. The surfaces tend to be extremely complex without any sense.