Fixed Constraint Failure on Spline

[MilesH]

Create a Spline using Reference Points and lock it using a Fixed Constraint. Draw a Line across it. Trim one side of the Line using the Trim Figure tool. What happens? For me, the Fixed Constraint is removed without warning and the trimming of the Line disturbs the shape of the Spline. Essentially, the Line is not trimmed to the Spline in its locked state and the process of adding the End Node of the Line to the Spline corrupts it. For a Spline created by Control Points or Interpolation Points, the Fixed Constraint is also removed without warning but the Line is trimmed correctly without disturbing the Spline curve.
I have V24. Please could someone verify this behaviour in V27? Thanks.

 

[stepalibre]

Try extend. Trim appear to be destructive to the fixed constraint. Perhaps it should warn?

 

[Stu3d]

Exactly the same in V27.
Extend does still remove the fixed constraint but the spline doesn't appear to change.

 

[stepalibre]

For a Spline created by Control Points or Interpolation Points, the Fixed Constraint is also removed without warning but the Line is trimmed correctly without disturbing the Spline curve.

I believe this is the correct behavior. In order to trim the constraint is dissolved for the trimming function. Perhaps it should warn the fixed constraint will be removed? It could also reapply the fixed constraint to the input curve after trimming.

Spline using Reference Points

The reference points defined the spline. Trimming to it breaks the constraint and adds a new reference point at the trimmed point. This will change the shape of the input spline.

 

[MilesH]

Trimming to it breaks the constraint and adds a new node at the trimmed point. This will change the shape of the input spline.

But you can add a Node without changing the shape of the Spline... Edit, I see you can't....

 

[stepalibre]

Exactly the same in V27.
Extend does still remove the fixed constraint but the spline doesn't appear to change.

This is true for unconstrained splines.

 

[stepalibre]

But you can add a Node without changing the shape of the Spline...

For by Control Points or Interpolation Points splines.

 

[stepalibre]

Perhaps the command should warn. Aside from that the spline behavior is correct.

side note:



Is the spline missing a message as shown for arcs?

 

[MilesH]

For by Control Points or Interpolation Points splines.

Indeed, so why does the Fixed Constraint need to be removed for those?

 

[MilesH]

I still don't understand why Extend doesn't need to change the Spline curve yet Trim does (using Spline by Reference Points)...

 

[stepalibre]

Indeed, so why does the Fixed Constraint need to be removed for those?

It doesn't. The Fixed Constraint can be reapplied to the input curves after using the trim function, with the API.

I still don't understand why Extend doesn't change the curve but Trim does...

This might be a bug or a feature. What I see is trim is destructive and extend is not for reference point curves.
There's also a difference in how the trimmed and extended line interacts with the spline after the operation.

 

[MilesH]

This might be a bug or a feature. What I see is trim is destructive and extend is not for reference point curves.
There's also a difference in how the trimmed and extended line interacts with the spline after the operation.

I'd love to see an explanation of this. Is it determined by the solver in 2D DCM or by its implementation in Alibre?

 

[stepalibre]

I'd love to see an explanation of this. Is it determined by the solver in 2D DCM or by its implementation in Alibre?

Me too. My guess is Alibre. I know it's possible to break the entities at the intersection point or a split operation of the line and not the spline. Many ways to trim to a spline in a non-destructive way.

Edit: The side you choose to trim can also replicate the extend operation.

 

[MilesH]

I guess that too. I think this is a bug in Alibre. I can't think of any reason for it to be a feature or for the Fixed Constraint to be removed, certainly not for Control Point or Interpolation Point Splines and certainly not without warning.
You can also drag the End Node of a Line onto a Reference Point Spline, without disturbing the curve.

 

[MilesH]

Edit: The side you choose to trim can also replicate the extend operation.

Unless I misunderstand you, I can't replicate that. Try a Line crossing very close to a Reference Point.

 

[stepalibre]

Unless I misunderstand you, I can't replicate that. Try a Line crossing very close to a Reference Point.

I mean in the algorithm when the feature is made. Similar to a trim and extend command, as programs have.

quick change checker - to test the change in the spline extend vs trim

 

[MilesH]

I mean in the algorithm when the feature is made. Similar to a trim and extend command, as programs have.

Understood. Thanks!