## geopdes-users

 [Geopdes-users] Control Points weights interpretation of "nrbkntplt" routine From: Marco Brino - 2012-06-20 16:42:38 ```Hi all, I'm very new to NURBS and IGA, and I'm facing to very simple problems... While understanding the NURBS structure, I found problems on weights. In particular, for a quarter of circular surface, using degree of 2 along the circular coordinate, and 1 along the radial coordinate (like explained in prof. Hughes' IGA book, chapter 2, "bent pipe"), I could place three control points for the external edge ( [-1 0 0] [-1 -1 0] [0 -1 0] ) and the other three coincident at [0 0 0]. Well, in order of having a circle, the weight of control point [-1 -1 0] should be 1/sqrt(2), but instead of "bending" the edge towards the center, is "bent" towards the outside... Am I doing something wrong? I had the same problem while defining the hole "bent pipe" example on prof. Hughes' book, and all the edges were bent towards outside. Thank you very much for your help. Regards, Marco -- Marco Brino Politecnico di Torino - DIGEP Corso Duca degli Abruzzi, 24 I-10129 Torino, Italy +39 011 090 7205 +39 393 554 4537 marco.brino@... ```
 Re: [Geopdes-users] Control Points weights interpretation of "nrbkntplt" routine From: Rafael Vázquez - 2012-06-21 11:40:38 ```Hi Marco, some people had the same problem before. Usually in the papers you will see the projected control points, but the NURBS toolbox works with the weighted control points. This means that you have to multiply the coordinates of each control point by its corresponding weight. It is explained (a little bit) in the appendix of the article, and in more detail in the NURBS book. Regards, Rafa ```
 Re: [Geopdes-users] Control Points weights interpretation of "nrbkntplt" routine From: Marco Brino - 2012-06-21 12:52:53 ```Thank you very much, Rafa! Now I got it! Sorry for the very low level question, but I'm just getting little problems like that!! Regards, Marco On 21/06/2012 13:23, Rafael Vázquez wrote: > Hi Marco, > some people had the same problem before. Usually in the papers you will > see the projected control points, but the NURBS toolbox works with the > weighted control points. This means that you have to multiply the > coordinates of each control point by its corresponding weight. It is > explained (a little bit) in the appendix of the article, and in more > detail in the NURBS book. > > Regards, > Rafa > > -- Marco Brino Politecnico di Torino - DIGEP Corso Duca degli Abruzzi, 24 I-10129 Torino, Italy +39 011 090 7205 +39 393 554 4537 marco.brino@... ```

No, thanks