approximate copy creating uneven curvatur

[cloughna]

If I sketch an arc with a tangent line (total of two
segments) and then do an approx copy of them, something
weird happens.

If I do a curvature plot of just the line and arc, i have
a constant curvature on the arc and zero curvature on the
line (like you would expect)

If I then however create the approximate copy, the
curvature exhibits a 'damped' response after the
transition from the arc to the line.

Thoughts?

 

[solidworm]

approximate copy, is a spline approximation of the selected sketch entities and is a curvature continuous spline.how do you expect the curvature to be?

Edited by: solidworm

 

[cloughna]

I suppose I would like the curvature to go down to zero at
the vertex between the line and the arc.

I would define that as continuous... a nonzero value along
the arc, and then zero afterwards.

If that's unclear, create a spline that is C2 to a line
(using the 'equal to' constraint) and then look at the
curvature plot of those two entities. THAT it what I would
like to replicate using approximate copy.

 

[solidworm]

the damping oscillation is a behavior of a spline with too many points.
you can see the number of spline points of the approximation curve if you goto (Tools>Debug>Geom debug>Dump Entity), in my case it was 28.
View attachment 5130
if you try to manually trace it with a spline with the same number of points,you'll get the same damping effect.





Edited by: solidworm

 

[cloughna]

Wow, thanks. I had never seen that.

It looks like it's just a reporting tool, I imagine there
is no way to control the number of points in the approx
spline other than changing the underlying geometry?

 

[solidworm]

yes,its it's a reporting tool.
there's no way of changing the approxomation tolerance or the number of spline points, as far as i know, in ProE.

 

[cloughna]

Im in WF5.0 and can't seem to find the path you described.
There is no 'debug' under Tools.

I'm in WF5, what version are you in?

 

[solidworm]

wildfire 5, M070. it was in previous versions too. its the last item in tools menu.

View attachment 5131

 

[cloughna]

weird, i don't have it. My tree ends at 'Options'

I'll have to look into it.

Also, i've got a workaround (potentially) to my initial
problem.

The problem I had was that I wanted C2, but also wanted
control (a 'C' constraint on a spline wasn't enough).
Ideally that would have meant lines and arcs and then an
approx copy, but I've found that I can get away with
using a control polygon on the spline.

If I make the first two arms of the control polygon
colinear with the line with which I want C2, I get a
curvature plot that goes down to zero at the vertex.

Control polygon isn't as easy to control as lines and
arcs, but certainly more than a loose spline.

 

[solidworm]

maybe "debug" is part of pro/toolkit.
yeah,this was the relation (thanks to jeff), it's true for a 2 point spline (4 control vertices), if b=0, k(curvature at spline endpoint p) will be 0.
this special case (b=0) seems to be true for a spline with any number of points.
View attachment 5132

here's a screenshot of the approximate curve points: (using debug)
View attachment 5133







Edited by: solidworm

 

[solidworm]

another thing i have noticed using debug tool is that the edges that make up the boundary of a surface,do not have the same number of points as the curves used to build the surface. for example this boundary blend is made between two 3 point splines, but the edges that coincide with those curves, have alot more points:
View attachment 5134

 

[design-engine]

Approximate copy should have a slider in the interface so users can approximate the approximate.