area class a

[catapulta00]

Hello everyone

I would like to know if pro/e is able to create class surfaces with continuity c3. example if I put the curvature bond between two splines I get a result as in the image, it doesn't seem like a g2 continuity, it can become if I work on it but so doing I can also become a g3 continuity to the eye. and with the surface the result is even worse. What I wonder is whether the curves created in the isdx module are fake or not.

all your advice or experience and well come.

Thank you.

 

[Fulvio Romano]

mmmhh... There's some confusion. . .
a class surface does not imply any continuity. a class surface is defined as "beautiful to see" and that "beautiful", but it is not a more precise definition of that. If we really want to do lazy, stealth is made of class surfaces a.

the diagram you see is a curved diagram, that is a second derivative defined on curvilinear ascissa. the curve is continuous (has no jumps), so the c2 is confirmed. the fracture you see is a discontinuity of the derivative of that diagram, and therefore is a c3 discontinuity.

it is possible to have cx continuity with x to pleasure simply by manually aligning the cvs of the nurbs, therefore not to the eye. By the way, the automatic tangency command puts the surfaces in tangency, but nothing tells you about the length of this tangency, so to have class surfaces to, to work on the cvs (certainly curves, but sometimes even on those of the surfaces) is obligatory.

 

[catapulta00]

fulvio you who are strong in mathematics clarify some things to me, is it right that to make two g3 continuity curves serve 7 cv's? and if it is true enough then to create the relative control points on the spline, but then I become mad to change that spline to make the curvature tangent and continuous, or is there a trick in pro/e? And lastly, I know that it is long history but just a hint, the difference between spline surface, bspline, and bezier, in order to create two beautiful smooth surfaces.

Thank you.
If you answer me, you're great.

 

[maxopus]

I don't understand what you mean by g3. g1 is the continuity in tangency, g2 in curvature... and g3?
I don't know if it's possible, but I never used it.
class a is also subject to interpretations, as there is no unique definition.
For example, there is a famous German group that defines surface tolerances in class compared to theoretical curves.
I model for the automotive and don't give a damn about the class a.
I know only that I have to shape correct surfaces without flexo points.
in isdx it is necessary to use curves at very few knots (preferably only the two terminals) in rex use surfaces bezier 3x3.
I follow the old method that always works, very low-grade surfaces and curves joined together.

 

[catapulta00]

g3 is in accelerated cost, i.e. the curve plot comes to you without peaks

 

[maxopus]

g3 is in accelerated cost, i.e. the curve plot comes to you without peaks

and what do you need, of grace

 

[Fulvio Romano]

fulvio you who are strong in mathematics clarify some things to me, is it right that to make two g3 continuity curves serve 7 cv's? and if it is true enough then to create the relative control points on the spline, but then I become mad to change that spline to make the curvature tangent and continuous, or is there a trick in pro/e? And lastly, I know that it is long history but just a hint, the difference between spline surface, bspline, and bezier, in order to create two beautiful smooth surfaces.

Thank you.
If you answer me, you're great.

First of all I did not understand if you are trying to move the cp (control points, for which passes the curve) or the cv (checking tactics of the control range). I would strongly recommend the cv... but the various software make some confusion between points and vertices, sometimes points are called knots and vertices, points. depends on software.

I'm sorry, but I got into a proe discussion, but I don't know proe. so what I say is generic and not specific of the program.
I always use and only nurbs, which are a kind of bspline, and are the most manageable. I try to make a quick excursus, but I should study it, because I remember very little.
bezier curves are polynomials to a parameter and weightless, very simple to handle, but practically unusable to realize complex forms.
splines exceed the problem of polynomial, because they are made up of more polynomials. This means that if I add a point I don't have to change the degree of polynomial (as in the case of beziers), but I have to add another polynomial and "remember" by imposing the conditions on the contour.
b-spline and nurbs are evolutions of the spline. allow away a greater independence of a section of the curve from the adjacent ones. for example with spline it is not possible to make a circle arc or a parable, instead with a nurbs yes. the nurbs have more "leve" to be changed because it is possible to change the weights of the different points, even if I never happened to have the need to change such weights.

p.s. why 7 cvs? a point lined by c1, two by c2, and so on, no?

 

[Fulvio Romano]

in isdx it is necessary to use curves at very few knots (preferably only the two terminals) in rex use surfaces bezier 3x3.
I follow the old method that always works, very low-grade surfaces and curves joined together.

I always use and only nurbs, which are a kind of bspline, and are the most manageable.

oooppss.. .

I'm just personal, but I would not recommend the max method. If the curve is very complex, with so many pieces of curves you can't harmoniously follow the entire surface. however depends on the habit and the software used.

 

[Parametric_Ozzy]

and think that you can get up to the degree of continuity g5!!! :smile:

 

[catapulta00]

max i need to make beautiful surfaces with a reflection of the Madonna; But this makes me rous because I thought that pro/e had some tips to make my vice simpler instead no, however remains a bomb. I thank you both for the advice and clarification.

 

[Parametric_Ozzy]

max i need to make beautiful surfaces with a reflection of the Madonna; But this makes me rous because I thought that pro/e had some tips to make my vice simpler instead no, however remains a bomb. I thank you both for the advice and clarification.

g2 is more than enough to make surfaces with a reflection of the Madonna, if not use blender or rhinoceros.
One thing that perhaps escapes, however, is that we must also have the tools to verify this type of continuity.
greetings

 

[maxopus]

I don't make surfaces with so many pieces... at every corner limit a surface.
the control of a surface with too many knots I leave it to others

 

[catapulta00]

Max tell me something: you can put the curvature bond between two splines, with more than 2 control points, and then click the control command of the spline by vertices, and/or vice versa; this in isdx environment.

 

[catapulta00]

what do you mean to have the tools to verify continuity?

 

[Parametric_Ozzy]

what do you mean to have the tools to verify continuity?

analysis tools and productive tools. . .
It will be necessary to produce blessed surfaces, no?:smile:

 

[maxopus]

I'm a little intrigued, guys... I'll take the speech tomorrow.

 

[enri]

so that max "disintrippa" maybe we give (also I, because after g2 I miss ) a look qui, a link I had kept, because I was interested in the topic, on the difference between the quality of the surfaces obtained with alias and rhino, so maybe the most experienced on the g (not the point I recommend, would be ot even if interesting... :ddd ) explain the matter well.

 

[catapulta00]

che ne pensate di questa definizione a me sembra un po eccessiva

understanding class a surfaces:

1. the fillets - generally for class a, the requirement is curvature continuous and uniform flow of flow lines from fillet to parent surface value of 0.005 or better (position 0.001mm and tangency to about 0.016 degrees).

2. the flow of the highlight lines - the lines should form a uniform family of lines. gradually widening or narrowing but in general never pinching in and out.

3. the control points should form a very ordered structure - again varying in angle from one row to the next in a gradual manner (this will yield the good highlights required).

4. for a class a model the fillet boundary should be edited and moved to form a gentle line - and then re-matched into the base surface.

5. matched iso-params in u & v direction are also a good representation of class a.
6. the degree (order) of the bezier fillets should generally be about 6 (also for arc radius direction) sometimes you may have to go higher.

7. also you have to take care of draft angle, symmetry, gaps and matching of surfaces created with parent or reference surfaces.

8. curvature cross-section needles across the part - we make sure the rate of change of curvature (or the flow of the capping line across the top of the part) is very gentle and well behaved
http://catiatutor.com/basic/catia-handbook/class-a-surfacing.html

 

[maxopus]

che ne pensate di questa definizione a me sembra un po eccessiva

understanding class a surfaces:

1. the fillets - generally for class a, the requirement is curvature continuous and uniform flow of flow lines from fillet to parent surface value of 0.005 or better (position 0.001mm and tangency to about 0.016 degrees).

2. the flow of the highlight lines - the lines should form a uniform family of lines. gradually widening or narrowing but in general never pinching in and out.

3. the control points should form a very ordered structure - again varying in angle from one row to the next in a gradual manner (this will yield the good highlights required).

4. for a class a model the fillet boundary should be edited and moved to form a gentle line - and then re-matched into the base surface.

5. matched iso-params in u & v direction are also a good representation of class a.
6. the degree (order) of the bezier fillets should generally be about 6 (also for arc radius direction) sometimes you may have to go higher.

7. also you have to take care of draft angle, symmetry, gaps and matching of surfaces created with parent or reference surfaces.

8. curvature cross-section needles across the part - we make sure the rate of change of curvature (or the flow of the capping line across the top of the part) is very gentle and well behaved
http://catiatutor.com/basic/catia-handbook/class-a-surfacing.html

as you see it is not about continuity in terms of degree.
I have been working for years doing reverse and I have never used continuity degrees higher than that of curvature.
roundings (round) in pro/e are mainly curved using the specific function, as in the same there is the option for the conical section and you can attribute to them the continuity in curvature.
If you ask fiat you will have a different definition, if you ask volkswagen you will have another one.
at the end of the fair you must keep in mind that, all you do goes under a milling for the realization of a mold and ask for micrometric precision in the scaffolding does not make any sense, because everything would be lost in mechanical processing.
the isdx module do not use it (even if I know it), as soon as I can take a look and let you know which are the degrees of continuity that can be used for curves.
with the rex module you work differently, using mainly and directly the surfaces and curves serve only for some types of connection and for some cuts.

 

[Fulvio Romano]

I agree with what he says max. micrometric precision in the joint of the surfaces serves from a mathematical point of view for the program that makes the tool path, but little to see with the brake physics.
Besides if you are modeling a mouse or ship, you will realize that talking about errors generically expressed in fractions of millimeter does not make much sense. an error of a centimeter on the belt line of a ship can be less severe than half a millimeter on a mouse style curve.

Finally... the fillet...
We distinguish technical rays from style rays. style ones are never done with the "fillet" function of the programs, because point-by-point must be checked.