closing NURBS curve / NURBS cylinder tangent discontinuity - Polyloop

f.ip2 · 26th July 2004, 02:42

hi i have a serious problem understanding amapi.

i draw a spline close it but than it does not get closed only the eding points get aligned. so i end up with a disrupted curve flow.

how can i close a nurbs curve so the curve flow is smooth?

also i translated the CVs of a nurbs cylinder and i saw a similar problem.
IMHO i never saw this NURBS behavior in any CAD app i used so far so
i dont know whats wrong. when i change one CV i expect the the profile of the cylinder cap is still smooth.

any tip?

also can somebody explain me how to align two circles so they match in x,y or z? i just can get it to work. even read the manual.

claas

Thomas · 26th July 2004, 11:03

Amapi is only a surface modeler, then, if you move one edge of your cylinder, the cap won't move the same... If you wan't to, you have to go to the lower level of the DG, séléct bot contole vertextes (from the cap and cylinder), select the common edge or vertexes to move, and stretch them...
I know, it's a looong process, too long one.

About the curves, if they are closed, you can stretch them without opening them... but if you use the strange bezier handles near the connected controle points, it can open the curve. It's not a bug, it's a feature, which I don't agree with. To avoid it, you must use a snap controle point (the icon near the bezier controle in the stretch tool).
I just tested it, it works

f.ip2 · 26th July 2004, 12:12

ah ok

i somehow disagree with you as well that this is a feature. also this has nothing to do with surface or volume modeler. blender maya pixels 3d all can close a spline/nurbscurve so can illustrator and freehand do. its all the same math behind it.

for me not beeing able to close a spline in a smooth way this is a very big problem since i work a lot with profiles for lofting and extrusion, sweeping.

to avoid it i would need to ceate a circle add points and than model the shape i need. than i have a closed surface/spline.

claas

Thomas · 26th July 2004, 12:16

It was a long fight from me against the dev team... I lost this battle. but not the war ;)
You support will help me ;)

f.ip2 · 26th July 2004, 14:15

how can you fight about it?

for me this looks like a tangent discontinuity. something i honestly dont know from any other application i use. when they defend this as a feature i would say they dont know what they are talking about. nurbs is about smooth curvature flow. with weighting cvs you can change the flow a bit to include sharp and smooth edges/shapes in a nurbs spline/patch.

so when i create a nurbs circle and than i cannot move all cvs as i wish because i will get sharp edges i cannot smooth than we are not talking about nurbs. funny that poly lines can be closed smooth and they behave like i expected nurbs curves to behave.

this actualy makes me pretty mad because this was always the point why i ignored amapis nurbs tools in the older versions. sad that this is not changed in the current version.

why did they go this way? what is their reason?

claas

Thomas · 26th July 2004, 14:59

For me, when I say it's a feature, it's about the tangent handle which move the connection point (at last, I think it was think about opencurves and not closed curves) and I don't agree with this as a feature... I wan't speaking about the circle problem (I didn't understand this the first time)
I'll check it with the dev team next week.
Thanks again for your support ;)

26th July 2004, 02:42	#1 (permalink)
f.ip2 Vertex Join Date: Jul 2004 Posts: 22	closing NURBS curve / NURBS cylinder tangent discontinuity hi i have a serious problem understanding amapi. i draw a spline close it but than it does not get closed only the eding points get aligned. so i end up with a disrupted curve flow. how can i close a nurbs curve so the curve flow is smooth? also i translated the CVs of a nurbs cylinder and i saw a similar problem. IMHO i never saw this NURBS behavior in any CAD app i used so far so i dont know whats wrong. when i change one CV i expect the the profile of the cylinder cap is still smooth. any tip? also can somebody explain me how to align two circles so they match in x,y or z? i just can get it to work. even read the manual. claas Attached Thumbnails

26th July 2004, 11:03	#2 (permalink)
Thomas Always learning new stuff Join Date: Jul 2002 Location: Merignac, France Posts: 11,319	Amapi is only a surface modeler, then, if you move one edge of your cylinder, the cap won't move the same... If you wan't to, you have to go to the lower level of the DG, séléct bot contole vertextes (from the cap and cylinder), select the common edge or vertexes to move, and stretch them... I know, it's a looong process, too long one. About the curves, if they are closed, you can stretch them without opening them... but if you use the strange bezier handles near the connected controle points, it can open the curve. It's not a bug, it's a feature, which I don't agree with. To avoid it, you must use a snap controle point (the icon near the bezier controle in the stretch tool). I just tested it, it works __________________ Polyloop owner & Administrator - no support by PM or email. Polyloop [EN/FR] - Meuuh [FR +16 ans] - Totyo [FR] - Pixologic [JOB] - Le ZBlog [JOB] - La3dpourlesnuls [FR]

26th July 2004, 12:16	#4 (permalink)
Thomas Always learning new stuff Join Date: Jul 2002 Location: Merignac, France Posts: 11,319	It was a long fight from me against the dev team... I lost this battle. but not the war ;) You support will help me ;) __________________ Polyloop owner & Administrator - no support by PM or email. Polyloop [EN/FR] - Meuuh [FR +16 ans] - Totyo [FR] - Pixologic [JOB] - Le ZBlog [JOB] - La3dpourlesnuls [FR]

26th July 2004, 14:59	#6 (permalink)
Thomas Always learning new stuff Join Date: Jul 2002 Location: Merignac, France Posts: 11,319	For me, when I say it's a feature, it's about the tangent handle which move the connection point (at last, I think it was think about opencurves and not closed curves) and I don't agree with this as a feature... I wan't speaking about the circle problem (I didn't understand this the first time) I'll check it with the dev team next week. Thanks again for your support ;) __________________ Polyloop owner & Administrator - no support by PM or email. Polyloop [EN/FR] - Meuuh [FR +16 ans] - Totyo [FR] - Pixologic [JOB] - Le ZBlog [JOB] - La3dpourlesnuls [FR]

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26th July 2004, 12:12	#3 (permalink)
f.ip2 Vertex Join Date: Jul 2004 Posts: 22	ah ok i somehow disagree with you as well that this is a feature. also this has nothing to do with surface or volume modeler. blender maya pixels 3d all can close a spline/nurbscurve so can illustrator and freehand do. its all the same math behind it. for me not beeing able to close a spline in a smooth way this is a very big problem since i work a lot with profiles for lofting and extrusion, sweeping. to avoid it i would need to ceate a circle add points and than model the shape i need. than i have a closed surface/spline. claas

26th July 2004, 14:15	#5 (permalink)
f.ip2 Vertex Join Date: Jul 2004 Posts: 22	how can you fight about it? for me this looks like a tangent discontinuity. something i honestly dont know from any other application i use. when they defend this as a feature i would say they dont know what they are talking about. nurbs is about smooth curvature flow. with weighting cvs you can change the flow a bit to include sharp and smooth edges/shapes in a nurbs spline/patch. so when i create a nurbs circle and than i cannot move all cvs as i wish because i will get sharp edges i cannot smooth than we are not talking about nurbs. funny that poly lines can be closed smooth and they behave like i expected nurbs curves to behave. this actualy makes me pretty mad because this was always the point why i ignored amapis nurbs tools in the older versions. sad that this is not changed in the current version. why did they go this way? what is their reason? claas