Rhino Tutorial: Info on Knots (NURBS)

[@luke_fabis]

Thank you for tackling this. Not enough people really dive into this information, but it’s pretty close to essential. I really appreciate the work you do.

[@simpernchong]

Thanks 😁

[@mitchelthinks]

good video, you always post such good stuff

[@simpernchong]

Thanks for the visit

[@mingsumkwan2873]

Hi, so what's the benefit of inserting knot? even though it won't change the shape of the curve, the curve added a control point while the degree remained the same, resulting in a nonsingle span curve (which is not ideal).

[@simpernchong]

For building enough control points to modify the shape.. Not all situation require single span..especially for consumer product design. Insert knot and remove knots are 2 processes that i often use to rearrange the distribution of control points for controlled refinement of NURBS curves and surfaces.

[@simpernchong]

Can watch this demo for application of knot control on surfaces kzbin.info/www/bejne/Y2LKYoaQgNFpeqMsi=2ohmVW8Xsz45dgRM I am aware of rhino's non class A tools and hence a need to work around those limitations.

[@aminkasem8213]

can you tell me please how can i merge surface to only just 1 surface after convert stl to sub and tonurbes i need to convert result surfaces to one surface beacause powermill program doesn't read multi surfaces it need only one surface for example loft feature do you anderstand me please help me

[@simpernchong]

Oh... that is going to be very difficult. For simple form, you can try to Explode the model, then use MergeSrf to merge adjacent pairs of surfaces. But for complex form with mulitple topology flow.. it may not work.

[@aminkasem8213]

@@simpernchong Thanks for answer put its really not work in complex furniture leg and I can't merge it or join it in one Surface to Program Surface in powerMill

[@ber9474]

what is the use of knowing the number of knots？Thanks.

[@simpernchong]

Just my opinion.. the first part of the video where i count the number of knots is just to illustrate the concept. I guess, we don't really need to count it. The more important thing is to remove overlapping knots or multi knot as they can create discontinuity in curve smoothness. For high quality surface modelling, it is essential. Basically, we will want to use as best as possible, the least amount of knots and control points to express the form.

[@ber9474]

@@simpernchong Does knot have anything to do with the structure lines of the generated faces?

[@simpernchong]

@@ber9474 eh....you mean isocurve? No. But if there is a discontinuity in the construction curve (mutiple knots), the resultant surface can break into separate pieces at the multiple knot point...and a thick line will appear on the surface.

[@ber9474]

​@@simpernchong Thank you for your reply and I hope you can do a video about degree, thanks.Sorry about the language question by the way.

[@simpernchong]

@@ber9474 You are welcome 😁Regarding Degree there is already a basic video about it kzbin.info/www/bejne/jWi7omOVg66phLs Thanks.