topic Re: Nurbs - in Libraries & objects

Nurbs -

Nader Belal — Mon, 09 Apr 2018 20:05:19 GMT

Hi everyone,

I was trying to take an adventures step to understand nurbs GDL commands, but then I found out that the GDL manual is pretty confusing ... so here goes my questions:

1- Nurbssurface

degree_u: degree of surface in the u parameter direction
degree_v: degree of surface in the v parameter direction
nu, nv: number of control points in u and v directions, greater than degree (not less than order) of then surface in given direction

a- I understand the concept of U,V & W, but how many Knot points in UV must I use to define correctly a nurbs surface ?
b- Suppose that the surface is a rectangular shape with a slight curve, does this mean I have to take 4 points :
(0,0), (0,1), (1,1), (1,0)?

Re: Nurbs -

poco2013 — Tue, 10 Apr 2018 13:59:06 GMT

Lacking help from more knowledgeable users which I am not:

A general definition of nurbs is:

#knots in knot vector = control points + order
assuming rectangle (points at corners) and quadratic order = 5 knots/vector as in:
(0,0,1,2,2)
minimum control points would be at corners unless you wanted more control - than add point in centers.
(0,0,0), (1,0,0), (0,1,0), (1,1,0) i believe that Archicad also requires a weight.

Re: Nurbs -

Piotr Dobrowolski — Tue, 10 Apr 2018 15:35:13 GMT

There is someone who figured it out ... there is one single object on Archiradar that claims using it - unfortunately it is locked.

The only way I think it is possible to figure it out now is to make some nurbs object in Rhino and import it as an object to AC (I am planning to do it but the lack of time prevents form it ;P)

Piotr

Re: Nurbs -

Nader Belal — Tue, 10 Apr 2018 18:26:30 GMT

Already tried that, the model changes to a mesh object

Re: Nurbs -

Piotr Dobrowolski — Wed, 11 Apr 2018 15:02:49 GMT

Moonlight wrote:
Already tried that, the model changes to a mesh object

Since ver 20 it creates the series of nurbs related comands in 3d script - however the input from Rhino has to be a nurbs object.

Piotr

Re: Nurbs -

Nader Belal — Wed, 11 Apr 2018 22:17:42 GMT

by Piotr Dobrowolski
Moonlight wrote:
Already tried that, the model changes to a mesh object

Since ver 20 it creates the series of nurbs related comands in 3d script - however the input from Rhino has to be a nurbs object.

No it doesn't, I have just tried that again after seeing your comment. It changes the body to a mesh using VERT, Edge & Pgon{2}

Re: Nurbs -

Nader Belal — Thu, 12 Apr 2018 22:36:13 GMT

Thank you all

I have got the answer from another source

The U & V value that were mentioned in the manual are that of the surface as whole and not at a specific loction.

Re: Nurbs -

poco2013 — Fri, 13 Apr 2018 04:43:32 GMT

FYI:
For any interested: attached is a nurbs file for a simple cube of degree 1 (linear).
It was quickly made in Rhino and imported very well in to Archicad.
As you would see adding more degrees to make a true nurb would really complicate even a simple object.

size = X: 9.438, Y: 10.686, Z:9.197
The zip file contains the Rhino , GDL, Object, pln files plus the text of the 3Dcode which would probably be of primary interest.

I see that the conversion to GDL code was fairly direct and illustrates the usage of the Archicad GDL Code.

Critical to the code is the direction of the various faces, surfaces etc. I found that just too confusing -- Don't have the patience, And there's no explanation in Archicad other than it has to be done.

I found it much easier to just configure in Rhino and than import -- You may want to do it directly in Archicad -- Good Luck,

Re: Nurbs -

Nader Belal — Sat, 14 Apr 2018 12:26:39 GMT

Ok,

How did you manage to save this object as nurbs in ArchiCAD ?

Re: Nurbs -

poco2013 — Sat, 14 Apr 2018 15:31:36 GMT

Export Rino object as Rino 3D Model - 3DM. - Using MAC Rhino release 5.
IN Archicad in a new project -- use File- open -- select Rhino 3D model

use fit window as the object may be in left field.

Then select and open Library & Object -- save selection as -- object

Can't help with Rhino as I'm not familar with it -- I prefer FormZ.

FYI: I talked with tech support and no one in USA TS is familar with the nurb GDL commands -- said It was added just to import Rhino files. But its pretty straight forward except I can't figure out the direction of the cutting curves. Edges and Faces -- OK. if you figure that out let me know. I might make a video later but this is so tedious to do, i doubt it's not worth just doing in Rhino -- Wish they supported FormZ?

Re: Nurbs -

Nader Belal — Tue, 17 Apr 2018 22:17:25 GMT

Thank you, with that I can continue my way

Re: Nurbs -

Nader Belal — Wed, 18 Apr 2018 14:36:06 GMT

@poco2013

well I started from zero, and I saw another problem, that I although my code was correct using Nurbscurve2D & Nurbscurve3d was correct, it always gave me a error that I have missing parameters.

And now I know why

ArchiCAD uses OpenGL nurbs
Rhino uses openNurbs nurbs

so as long you're aware of the differences, you will get to where you want to go