Planar Degree 3 Curves Convert to Line After Joining.Why? No Answer?

Hi Guys
I draw some straight interpolated curves. When I join them together, suddenly converted to lines. why this happens. I don’t want to convert. in Both Rhino 6 and Rhino 7 latest Update.

Question.3dm (360.4 KB)

I think they are being converted to polycurves. Taken from the Join command Help FIle, The introductory comment starts off with:

Join turns lines into polylines, curves into polycurves, surfaces and polysurfaces into polysurfaces or solids.

What do the Object Properties/Info panel have to say?

I’m just getting into this more deeply myself… so I’m no authority here. and I’m not sure what you should do to avoid this conversion from happening… except to suggest that maybe you can group them together.

Thank you for your answer!
My Degree 3 curves converted to degree 1 lines. very unusual! They have being changed to POLYLINE actually that is weird!

Two different behaviors:

Join command with nothing pre-selected
Select two “lines” which are degree 3 curves
Result is a polycurve with degree 3 segments

Select two or more “lines” which are degree 3 curves.
Join command
Result is a polyline


Thank you!
if the curves are not straight or planar, Result is a polycurve with degree 3 Segments. issue is with straight and planar curves. you are right. but do you think this is Normal?

My guess is that is the intended behavior. In many cases there is no advantage to keeping straight segments as other than degree 1 lines, and there can be disadvantages. I’m curious why you want to keep the segments as degree 3?

i would say just for sake of consistency if he wanted it a line then he would use simplifycrv command :slight_smile:

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it could be a bug. bcoz if you Rebuild More Than 4 Cps, they Remain correctly without any issue.
but this is my strategy to make a Periodic Profile for Single Surface Sweep for using in Surface Modeling. I always use this way.

A workaround is to _ChangeDegree the polyline to degree 3.

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ChangeDegree to degree 3 (or any degree > 1) used on a polyline results in a single curve with multiknots at the kinks, not a polycurve.


I don’t know why Mcneel Team members still didn’t give me a logical answer.

Because it’s Sunday? :roll_eyes:


Hello - I think this has come up before, and I do not recall the upshot, but off hand this looks incorrect for how V7 Join should behave. I’ll see what I can find out.

@opalword - I cannot repeat this now in our latest builds here - degree is maintained per segment…, so in fact it may have been fixed recently, though I do not see a bug track item for it.

It has not been fixed - there is still a bug - RH-64804 Join and polyline output


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Thank you Pascal!

RH-64804 is fixed in Rhino 7 Service Release 9