Spline issue

[drwtds]

Hi to all

Spline... is it really in this way? I hope not...

After couple of hours invested while playing with spline in ordinary Pro/E package, I am little confused, to say at least. The basic spline funcionality lacks that intuitive feel as SW represents(IMO).

I am specialy interested in creating curves on blueprints or scanned data with best accuracy as possible. I tried that with spline but it did not work to me as I was expacting it would.

As far as I am concerned Pro/E manage Splines as B-Splines(UPBS), right? Not as Nurbs?

More, I assume that default spline is 3 deg curve. Is there a way to rise the no of vertex in control polygonal(rise the spline degree above than 3?)?

I tried to follow the blueprints layouts, and 3d scanned data either, but it was really hard task to follow within only 3 deg spline Pro/E offers. I tried to introduce additional points(knots), but this affects with sh*ty curvature plot.

Later, I created couple of spline entities, joined together by tangent constraint, but this provides lack of constant curvature plot which is not what I want to obtain.

In the end I tried those extra menu > Point, Fit. I am still confused of using them. Has anybody used them with success?

So there are basic to me questions:

*how should I manage creating best curves on blueprints or scanned data(I really try to avoid importing any stuff from Alias, Rhino, etc)?

*what is deviation value expectable in consumer product the curve could have in comparison to scanned data?

*how can I mesure the deviation(differance) between created curve and scanned one?

*is there a way to check degree of scanned curve?

 

[mgnt8]

You create the best curves easily with ISDX but this is a more costly module.

Are you talking about spline or conic? The conic is 3 degree, but the spline can be as heavy as you want it. Double click on it and switch to 'Modify spline using control points'. I'm not sure about other CAD programs but I've found that in Pro/E the more cv's added, the rougher the the curvature becomes. I don't know why this would be different in SW. In order to use Fit, add some geometry lines near the polygon segments and when you select Fit, it will snap to the geometry. Curvature between splines can be achieved with Tangent constraint conbined with Equal constraint.

Finally, search on this site and google for jeff4136. He's the expert on bezier curves and b-splines and their use in the variable section sweep feature.

 

[drwtds]

hello mgnt8

conics arcs are not 3 deg curves, because of the definition which stays behind "degree" rule:

*curve degree is related to the no of control points -> No of CP[Pn] = N(degree)+1

so N= Pn-1

spline in Pro/E by default has 4 control points which gives us N=4-1=3

conic arc has 3 CP, so its degree is N= 3- 1 = 2

it can not be mixed with spline created with extra points. Each combined spline has than less Cp`s than standalone spline

this picture introduces it well

*upper spline contains extra point

*lower one is created by two seperate splines



anyway thx for input. I gonna search those jeff threads

 

[design-engine]

Pro/ENGINEER uses only 3 degree curve structures. Each extra edit point you drop in concievably creates an extra span (alias speak) or an extra knot in the curve.

Your quesion is general about splines and not relative to a specific curve your trying to recreate.

 

[mgnt8]

it can not be mixed with spline created with extra points. Each combined spline has than less Cp`s than standalone spline

My mistake, you are correct, conic is 2 degree. Also curvature constraint as I explained is only possible with spline and line or arc not spline & spline. It would seem that Pro/E Sketcher is not the best place for what you're trying to accomplish. Does SW have this capability with their basic feature creation?

There is a way to achieve curvature continuity between Sketcher splines and existing geometry. You can find it here

 

[drwtds]

Pro/ENGINEER uses only 3 degree curve structures. Each extra edit point you drop in concievably creates an extra span (alias speak) or an extra knot in the curve.



Your quesion is general about splines and not relative to a specific curve your trying to recreate.

accurate notice

well, in fact I treid to follow blueprints from Pontiac Solstice introduced on Some surface behaviour...

I do not know how that guy created curves on underlaying jpgs but I got a problem with this. I mean, it is hard to obtain same flow, shape and curvature plot as that one on pictures from Alias. Suppose higher degree spline was used in Alias.

The question is: Is it possible to match same quality or better avoid Pro/E while considering such job.

 

[Jacoolo]

I do not know how that guy created curves on underlaying jpgs

if I am considered I must say I did not dive so deep regarding underlaying curves. I made splines with extra points, which indeed represents sh*ty curvature.

 

[drwtds]

yea...that were You who I mentioned.

is there really such great differance between ISDX spline capabilities and those ones in Faundation package?

 

[tobbo]

Iwouldnt say so. One difference in manipulating splines is that in isdx , you can move several cv.s at the same time, but in a sketched spline, you can only move one at a time. (unless you constrian the cv.s to a construction line offcourse...)


Another thing about isdx is that its pretty easy and fast wayto create 3d curves.


But... i still makes most of my surfaces "outside" isdx, using VSS or BB and so on...


//Tobias
Edited by: tobbo

 

[drwtds]

that sounds intresting...

I`ve got a problem with Boundary Blend regarding following conditions



I am aware that 3 curves should be avoided, so I created first small surface with VSS and timed it. Then I made BB






the surface looks pretty weird. I made further investigation and each time I obtain strange surf by BB but better with VSS

BB-surf



VSS-surf



why those two surfaces are different if created on same conditions?

And how should I prepare first surf to solve this 3 curves BB?

 

[jsantangelo]

See if this helps

http://www.screencast.com/t/8MvQyDeI

http://www.screencast.com/t/8MvQyDeI

http://media.skoffer.com/d6cf6105cb9b109364b3fb7a427510c9.flv


http://media.skoffer.com/c0f29a3cead5c613ba726e68e97180f0.flv

 

[Jacoolo]

exactly that is the way I would solve this 3 curves boundary. Sweep surface is the best to trim it back.

As I start looking at You pictures I realized that special case You are trying to solve is related to proportions between curves. With these conditions I would switch to other side while making trimed base surf





or consider another trick regarding such shapes as creating 4 curves boundry from start. This provides one quilt which should be trimmed then to obtain desired shape

 

[mgnt8]

I mean, it is hard to obtain same flow, shape and curvature plot as that one on pictures from Alias. Suppose higher degree spline was used in Alias.

The question is: Is it possible to match same quality or better avoid Pro/E while considering such job.

First you were trying to match SW, now you want to match Alias?

Where ISDX does have an advantage is (like Tobias said) the better
manipulation and control of the curves. Realtime adjustments all at
once with the curvature displays always on pushing & tugging to
smooth out all those inflections. Now if you're talking about Class A where attention needs to be paid to the rate of change of the rate of change, Pro/E hasn't much control there.

Maybe someone out there with some Alias experience can chime in because this issue comes on from time to time. We're always told with Style to keep the curves as light as possible for best curvature, so higher order sounds to me like more opportunities screw things up. But there's obviously some way to control the derivatives & get the angels in the architecture dancing.

 

[drwtds]

never mention about Your previous girl, even if it was 3 hours long...

I forgot, SW is trouble spot here.

maybe if I would not be left alone to learn surfacing, then I would not ask questions of ignorance regarding it.

I know only as much as I was asking about.

ISDX seems to surpass ordinary curve capabilities in ease of tweaking with it, but it does not introduce higher degree, right?

 

[tobbo]

ISDX seems to surpass ordinary curve capabilities in ease of tweaking with it, but it does not introduce higher degree, right?


Right, isdx is still 3 degree curves...


//Tobias

 

[mgnt8]

But ISDX has new functionality as of WF 4 called Surface Edit that allows freeform manipulation which when used correctly can more easily yield G3 conditions.


ISDX SE, among other things, allows a proportional weight to the cv's so
to give more control of the speed of the surface during sculpting. This combined with curvature combs, theoretically at least, can get us closer to higher order quality. SE also increases & decreases cv's of the surface. So I guess (?) the curves's degrees don't change.

Its my understanding (as explained to me) that styling & sculpting programs like Alias don't constrain to the higher orders either but it depends on the skill & talent of the modeler. It makes sense - it would be too good to be true if you could just right-click on a surface & select 'Class A' or something like that.

One more thing - Import Data Doctor in WF 5 has all those surface editing tools as ISDX. I haven't gotten much of a chance to play round with it, but it looks like it gives you all the high end surface manipulation features in the foundation package (for import geometry only that is).



Edited by: mgnt8

 

[tobbo]

speaking of "surface edit " in Isdx, . If you set the hidden config :


advanced_style_surface_edit


to "yes" , you will have one more (useful) option to edit your surf with.


//Tobias
Edited by: tobbo

 

[drwtds]

btw

has anybody "discovered" yet how to build ordinary spline to pass three points?

I know that is is simple within Curve trough points but then there is no chance tp play with Tweak menu. Gush, why?



I tried to make surface by VSS, in such way that spline follows three trajectories, but to that I need to fix spline to all three trajs which seems to be no possible in sketcher





Do I miss something?

I know Pro/E itself has such funcionality. It is clear when simple 3 curves Boundary surface is created.





How do you guys solve cases?

 

[tobbo]

i dont see the problem, maybe i

 

[drwtds]

try to create spline with extra point to be driven by 3 trajectories and in addition have control over control polygon. Suppose You gonna fail.

Boundary Blend seem to handle with it, but I do not know how?