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Spline Start Tangent Issue

18 REPLIES 18
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Message 1 of 19
quam12
2825 Views, 18 Replies

Spline Start Tangent Issue

Hi there, 

 

I am trying to draw an interpolated spline and in old autocad pre 2011 you would specify your points then at the end you would specify your start and end tangents. 

 

Now with the new method that autocad now uses you pick your start point then immediately specify your start tangent which is fine however when I use the mouse to specify the start tangent no matter if I use a set distance to specify the size and direction or if i pick an arbitary point in space direction of the wanted tangency autocad seems to snap to some pre determined huge vector size that makes the spline unusable.

 

I have found a few workarounds but this is now annoying me and would love to know what I;m doing wrong.

 

I have found that if i specify a size of 1 by typing the number it works however this still doesnt explain why it keeps jumping to some pre determined size no matter what I do. 

 

Hopefully you guys can shed some light on this for me 

 

thanks in advance 

 

 

18 REPLIES 18
Message 2 of 19
JDMather
in reply to: quam12

Bump!

 

Interesting that this has not gotten any responses.

I tried to figure out the new way for a few minutes and gave up.

Last year a couple of my students figured it out, but I seldom use AutoCAD anymore - I forgot their solution.

 

Surely someone here knows the new technique.


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Message 3 of 19
JDMather
in reply to: JDMather

Bump #2.

 

Anyone?

I think it is broken in 2015.

End tangency seems to work fine, but I sure can't figure out how to get start tangency to work.

Am I going to have to go into the Help files to find something that should be trivially simple (and was for years and years)?


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Message 4 of 19
SEANT61
in reply to: JDMather

It looks like Knots = Chord and Knots = Square Root use improper scaling. Apparently, Knots = Uniform is the only option that scales correctly.  That may be the only predictable option. 

 

Of course, Chord and Square Root parameterization options have certain benefits - those may be offline until Autodesk produces a fix. 


************************************************************
May your cursor always snap to the location intended.
Message 5 of 19
JDMather
in reply to: SEANT61

Bump #3.

 

Doesn't look like Autodesk is going to respond to this one.

Maybe I just need some training.


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Message 6 of 19
hmsilva
in reply to: SEANT61

Not the anser you were waiting for, but perhaps something like this to do the trick.

Untested, I don't have AC2015 in this laptop...

 

(defun c:oldSPL nil
  (initcommandversion 1)
  (command "_.spline")
  (while (> (getvar 'cmdactive) 0)
    (command pause)
  )
  (princ)
)

 

OldSpl will call the old Spline command.

 

HTH

Henrique

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Message 7 of 19
TFieldsELM
in reply to: SEANT61

I was having the same problem with start tangent spline shooting off into the distance.

 

Setting the knots to uniform solution worked for me. However, not sure of ramifications of not using the other settings.

Message 8 of 19
SEANT61
in reply to: TFieldsELM

The difference between the various parameterization methods become more apparent based on the relative distance between FitPoints.  In the attached, the three methods were used on three similar, but varying, frames.  Notice the long span to short span transitions.  Notice the Control Vertice placement (Fit Data has been purged) required for the different methods to ensure the spline passes through the required points.

 

Splines are interpolations, i.e., a scheme to predict valus for unknown data.  Some data models are better represented with one parameterization method over another. 

 

For instance, consider the right most figure of my drawing, The SqrtChord method looks to be the most sensible.  If a race track were built that required the cars to pass through those points, SqrtChord produces the shortest track.  But, if the objective was to have the cars traverse the race in the shortest time, then the Chord method may be better. 

 

 


************************************************************
May your cursor always snap to the location intended.
Message 9 of 19
SEANT61
in reply to: SEANT61

Incidentally, if it turns out that the default ‘Chord’ method is the best, the routine posted by hmsilva is a great option.

************************************************************
May your cursor always snap to the location intended.
Message 10 of 19
hmsilva
in reply to: SEANT61


@SEANT61 wrote:
Incidentally, if it turns out that the default ‘Chord’ method is the best, the routine posted by hmsilva is a great option.

Hi SEANT61,

 

with a button, just

^C^C(command "_.spline")

 will do the trick.

 

Henrique

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Message 11 of 19
SEANT61
in reply to: hmsilva

Even better. 🙂

************************************************************
May your cursor always snap to the location intended.
Message 12 of 19
JDMather
in reply to: SEANT61


@SEANT61 wrote:
Even better. 🙂

Works fine for me in Autodesk Inventor.  Smiley Surprised


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Message 13 of 19
SEANT61
in reply to: JDMather

Does Inventor use the same methodology (Start-, EndTangent, Parameterization) for fit point spline creation?

************************************************************
May your cursor always snap to the location intended.
Message 14 of 19
JDMather
in reply to: SEANT61

No.

I can add tangent at any time (after creation).

 


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Message 15 of 19
SEANT61
in reply to: JDMather

"I can add tangent at any time (after creation)."

 

I suppose that's true for AutoCAD as well, via the Properties Panel.  When AutoCAD behaves, it should be easy to do it up front as well.

 

What about the parameterization options?


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May your cursor always snap to the location intended.
Message 16 of 19
nestly2
in reply to: SEANT61


SEANT61 wrote:

"I can add tangent at any time (after creation)."

 

.....I suppose that's true for AutoCAD as well, via the Properties Panel....


 Multifunctional Grips

 

Spline Mulitfunctional grips.gif

Message 17 of 19
SEANT61
in reply to: nestly2

There, too. 🙂


************************************************************
May your cursor always snap to the location intended.
Message 18 of 19
JDMather
in reply to: SEANT61


@SEANT61 wrote:

What about the parameterization options?


Inventor splines are fully parametric.  Can also us Equation Curves, 2D and 3D.

Also include handle (weight, and angle) and curvature controls and curvature comb display.


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Message 19 of 19
SEANT61
in reply to: JDMather

JD, our exchange has become somewhat disjointed.


I may not understand your reply 6 posts up:
“Works fine for me in Inventor”
That was a reply to my reply to hmsilva – “Even better.” The even better statement was in regard to the brevity of hmsilva’s command macro.

With regard to you latest reply; I’m sure Inventor offers all sorts of good parametric bindings, as well as numerous features to investigate and modify curvature. The parameterization I was referring to, though, was the Uniform, SqrtChord, Chord option similar to AutoCAD’s Fit Point Spline options.

 

Edit:

I suppose I should stop using "parameterization".  AutoCAD's spline command lists those options "Knots".


************************************************************
May your cursor always snap to the location intended.

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