Rhino/Grasshopper - Understanding the fundamentals of NURBS Geometry
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- Опубликовано: 21 окт 2024
- This tutorial will look at the fundamental concepts of what geometry is made up of in rhino and how we can use that to our advantage in grasshopper.
We'll look at some of the differences between Polylines, NURBS Curves, NURBS Surfaces, Polysurfaces/Breps and Meshes.
Rhino Documentation on openNURBS
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Such an amazing and so important tutorial ! Thanks for all these important informations
+Σταύρος Καραμπέτσος cheers!
Hi Daniel, first of all, thanks for your series of tutorials, they're great and I am following all of them. I would like to ask you a question about the spheres shown on this video: while trying to manipulate the control vertexes on "sphere degree 2", I have the same issue you encountered on minute 14:00. Then at min 14:45, you solved it in some way and show how it deforms producing a sharp edge. How did you set the sphere in order to behave that way? Thanks!
giacomo forcina hey Giacomo! What happens in that part of the tutorial is a really interesting 'problem'. You see, this is something I didn't understand until a little bit later, but when you create a sphere, by default, the geometry is closed, but there is seam there where the points don't interpolate across to create a smooth transition. I haven't looked into this too much (but I really should), so I'm not entirely sure of a good way to achieve this effect. The only way that I would know how to do it is to use the surface from points component on a collection of points that will form a closed volume, and ensure the interpolate samples boolean is set to false. Interestingly, you cannot create a lofted surface of this manner, if you use the option to create a closed loft, it will interpolate across that NURBS boundary. If you try to create a closed loft however, by having 2 curves on top of each other at the start/end point, the loft will inherently fail. What this leads me to assume is that this is exposing a flaw in NURBS geometry, as NURBS do not typically behave in this manner. Generally, if you want to create sharp edges on a NURBS object, you need to create it with multiple surfaces, and have junctions.
To answer your question more simply, I went through the undo history, and reverted back to the original degree 2 sphere.
If you are interested in creating sharp edges like this, you might need to look at t-splines, which has a 'crease' command - but as I described above, it creates creases by using multiple surfaces.
Thanks for the really interesting question though! I've been wondering if anyone would pick up on that soon.
important tutorial thanks for sharing !!
Great tutorial Daniel, im beggining in rhino and grasshopper an this one really help me. I only have one question if you can help me, Is there any way to convert a polysurface to surface? i noticed as you say in min 19:45 that grasshopper has more function with surfaces. Thanks!
It will entirely depend on your polysurface. By and large, there will not be any shortcut to doing so that I can provide. Some polysurfaces will literally be impossible to convert to a single surface because of a property known as the genus, essentially the amount of holes in the object. If the genus is greater than 1, you will have to work with a polysurface.
en.wikipedia.org/wiki/Genus_(mathematics)
Now that is not to say you can't use polysurfaces in a more clever way. As the name suggests, a polysurface is just a collection of surfaces - which can be broken down into individual surfaces and then manipulated/used to extract data.
I'm working on a tutorial on topology which will hopefully address surface and polysurface construction at some point, as I think these are very key areas that people tend to overlook when working in rhino.
Thanks for the great question, and I hope I answered it.
Thank you for the answer, also the videos I am watching all the others, they are really usefull