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C2 with control polygon

C

cloughna

New member
I have a spline that needs to be curvature continuous to an
adjacent line. It needs to be purely C2 (so no fudging it)
because it is a guide curve for a boundary blend that will
need to be C2.

I don't want to set the spline 'equal' to the spline to get
the continuity because I want to be able to play with
control polygon, so I can't use pro|e's 'C'constraint.

Any thoughts?
 
Hi
Pro/E
Wildfire enables designers to adjust curves with sliders and then
assign tangency and C2 matching to existing model surfaces, solid faces
and edges.
lets see, you need a sketcher csys a spline with at least 2 points

right click the spline ...modify then the file options will come up

points need to be in a .pts file formatsomething like;

00&nbs p;0
0.002408-0.0076950
0.009607-0.0155630
0.02153-0.022735&n bsp;0
0.03806-0.028997&n bsp;0

you want the end point of the pts file to jive with the endpoint of your spline before you import
 
well, that is no possible in sketcher. With one curvature constraint - yes. With both ends fixed - no.

Same happens to Datum Curve.

Solution - make a Boundary Blend surface - this tool allows to set both ends with Curvature transition and change plot of the surface. At the end copy side edge as a curve.
 
cant do that because of the 3deg curve limit....but ,


if its a "straight line" that you will attach your new spline to, then you caneasily locate your first and second controllpoint to make an curvature transition between the curves.


If its a "spline to a spline" , then you have to use a constructionline thats tangent to the first spline end to snap your controllpoints to. (of both of the splines = no good solution, but could be made)


But, since thenew spline will still only be 3deg curve, then you canonly do it on one side . If you could do a 5deg, then it would be possible to do it on both ends...


//Tobias
Edited by: tobbo
 
The boundary then copy approach works, but my problem is that i want to
use the curve to define the boundary blend...so copying it is less than ideal.

as far as snapping the control points to the tangent of the spline, i tried that.
And while the curve looked to be C2, the boundary blend was not picking up
on it, and failing when i tried to make the boundary constraint curvature.

I ended up just using ISDX to the curves and surface, but I prefer to stay in
the fully-controlled environment.
 
igot the "snapping controllpoint " to work.


Regarding isdx , i do a lot of my curves using isdx. There are ways to paramterically controll those curves too, it
 
Jeff did it with his Bezier curvature calculations. I don't know if the splines were technically C2 but the resulting sweeps were.
 
Yeah, I guess all those files were lost when the server crashed. I guess his method was lost along with it. Perhaps its for the best as it was terribly impractical when compared to the surfacing programs out there now.

Still it was pretty darned cool. That trajpar function constrained the splines together in a way that resulted in curvature continuous surfaces, but the real beauty of it was the way he defined the cv's with the equation. A simple algebraic definition brings elegant meaning to a volatile configuration of internal variables. Waves crashing on the ramparts yielding to a tranquility. Literally order out of chaos.
 
it is better not to manage those sort of constraints using sketcher. Sketcher tools should mature for this functionality and I have never emaield off my enhancment requests for Core modeling tools....

Use ISDX instead then utilize 'use edge' in sketcher to use that as sketch geometry.

I'm going to add that to my talk at 11:00 as part of my 20 tips and tricks.


Edited by: design-engine
 
I ended up using ISDX, and it worked well.

Still, I played around with it a little bit and came
across a not quite complete solution (for full
documentation check out
(http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/199
00012238_1990012238.pdf)



I found a way to make two different splines C2 to each
other within a sketch. The catch is that i need the
control polygon for each... meaning that it doesn't work
if one of the splines is a reference from another
feature.

Anyway, I did a quick camvid of it and put it here (skip
to the end for control polygon stuff, everything else is
just covering C0 and C1)

http://www.youtube.com/watch?v=3fHUNnJ76b4


If anyone does check out the video... thoughts on making
my curvature plot smooth? It's currently continuous but
not quite perfect. (to admin: if that's a topic for a
different thread I apologize).
 
so i've been reading old curvature threads and just
realized that the nasa link i found through google had been
posted by Jeff back in 08

sorry for the redundancy.
 
Nice bro, thanks for sharing. I love the old school constructions especially ratios. There's always interesting implications just beneath the surface.
 
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