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Questions tagged [nurbs]

NonUniform B-Spline (NURBS) is a method to describe parametric curves/surfece. TYpically used as base poriniteves in CAD modelling.

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4 votes
1 answer
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How to remove a control point from a NURBS curve?

I am trying to write an algorithm to remove a control point from a NURBS curve, similarly to what can be achieved using the CVREMOVE command in AutoCAD. I searched online but I was unable to find a ...
Lorenzo Celli's user avatar
2 votes
1 answer
147 views

How can I determine ideal NURBS surface control points for a multi-patch sphere?

I would like to know how to "parameterize" the control points for the 6 faces of the commonly used NURBS mutli-patch sphere ("Cobb sphere"), for an arbitrary-size control point ...
Chaosoahc's user avatar
0 votes
0 answers
103 views

Can STEP files contain polygon data? How do I get a smoother mesh out of a STEP file?

I am trying to work with a .STEP file I have received. Upon opening it in CAD Assistant, I find its surface as jagged lines, like a low poly model. When I export it as OBJ from there, the edges and ...
Bits168's user avatar
1 vote
1 answer
192 views

Matrix form of an open uniform cubic b-spline

I'm trying to find the matrix form for the equation of a cubic b-spline. More specifically, the "middle" part, S_i(t), is pretty straightforward and available everywhere: ...
fruity's user avatar
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3 votes
1 answer
76 views

Sweeping cross section along nurbs curve

I have a nurb/b-spline curve in 2d, and I want to sweep a cross section along it. Here is the curve and resulting "tube" (green points are control points): However, as you can see, the ...
lijas's user avatar
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1 vote
0 answers
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Geodesic approximation algorithms for minimal geodesic curvature

Introduction I am building an application in which given a surface and a pair of points on it, an analytic expression of some geodesic arc (preferably the one with the shortest length), between them ...
Stamatis's user avatar
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3 votes
1 answer
536 views

Determining Rational Quadratic Bezier Curve Weights for Circle

I am trying to create a spherical interpolation with 3 points. I'm currently using Quadratic Bezier Interpolation but have been told I should use Rational Quadratic Bezier Curve in order to get a ...
Dr. Pontchartrain's user avatar
2 votes
0 answers
43 views

Projecting a point on a Freefrom surface

My first issue is getting a set of planes and a set of points as input, an find the projection of the those points on the nearest plane. That was pretty easy, where i just calculate the normal of the ...
Mohbenay's user avatar
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0 votes
1 answer
544 views

Problems with Subdivision Surfaces

It sounds like Subdivision Surfaces are better than NURBS but not as good as T-splines. I would like to know some of the disadvantages of Subdivision Surfaces, what they can't do or what they do ...
Lance's user avatar
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3 votes
1 answer
196 views

drawing NURBS: knots, multiplicity, divide by zero?

I'm trying to grasp how NURBS curves work. I think I understand the principle, but I'm unsure about the formula. Here, I base myself on this course. From a DXF file, I got the following parameters: <...
tgirod's user avatar
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1 vote
1 answer
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B spline curve generation in Python

I am using the de boors algorithm to generate B splines in python. However I am getting spikes in the final figure. I do not understand why this happens. I am posting my code here for reference <...
Jose Kurian's user avatar
1 vote
1 answer
175 views

How does the Lane Riesenfeld algorithm work?

I understand de Casteljau's algorithm and I am familiar although not fully experienced with B-Splines. I am trying to understand the geometric interpretation of B-splines through the algorithm (just ...
Makogan's user avatar
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3 votes
1 answer
587 views

Normalize NURBS knot vector

I have NURBS surface data. I have a list of control points, knot vectors in U and V params and the degree. The U knot vector lies in range -3.14 to 3.14 and the knot V vector lies in range -100 to 100....
Vaibhav's user avatar
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5 votes
1 answer
463 views

How do CAD programs render non-polygonal 3D objects?

How CAD programs handle displaying B-Reps and NURBS/T-Splines in their viewports? Assuming viewport uses OpenGL API - are those programs transform every object into triangles and creating/deleting ...
pmakal's user avatar
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6 votes
1 answer
368 views

How to sample 3D points to visualize a B-spline surface?

Given that I have implemented a function called calc_bspline_surf() in C, and that function has the following declaration: ...
xyz's user avatar
  • 161
4 votes
0 answers
64 views

Making surface with common parametrization from bunch of other surfaces

I have bunch of surfaces, like in these two images: Currently to make single surface with common parametrization I sample points uniformly from all source surfaces, and fit single NURBS surface from ...
Ibraim Ganiev's user avatar
8 votes
1 answer
376 views

NURBS topology classification

In what sense is it true that a NURBS surface can only have the topology of a plane, cylinder or torus? For example I can do a NURBS sphere. Is the sphere homeomorphic to one of the above surfaces?
Valerio's user avatar
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8 votes
1 answer
2k views

NURBS knot multiplicity

In Splitting of NURBS curves there the answer relied on "maximum knot multiplicity". In order not to mix-up different topics I would like to kindly ask to answer it in another question: what is this "...
Ecir Hana's user avatar
  • 1,459
9 votes
1 answer
2k views

Splitting of NURBS curves

Splitting Bezier curve into two parts at some parameter t is easy thanks to De Casteljau's algorithm. Is there a similar algorithm for NURBS curves? How to split a ...
Ecir Hana's user avatar
  • 1,459
7 votes
1 answer
711 views

NURBS curve drawing

How to draw a NURBS curve? Compared with Bezier curve, I just evaluate the Bernstein polynomial, multiply it with control point positions and that's it. Looking at the "General form of a NURBS curve"...
Ecir Hana's user avatar
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6 votes
1 answer
550 views

NURBS curve offset

One of the benefits of NURBS curve over, say Bezier curve, is the ability to create offset curves exactly. How to proceed with such computation? Do I just translate the control points?
Ecir Hana's user avatar
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10 votes
1 answer
2k views

Non-uniform rational B-spline (NURBS) Basics

I'm trying to understand NURBS curves (surfaces later!) but I have some trouble understanding the very basics of its inner workings. Could someone please explain a few things to me? As I come from ...
Ecir Hana's user avatar
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