where did this extra copy come from?

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rek
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where did this extra copy come from?

Post by rek »

FreeCAD 0.19

In the process of undo/redo an extra copy of my geometry showed up and it persists on file save, but I don't see it in the Tree. Any Ideas where in the tree this dual copy of this geometry is hiding? I don't want to call it a bug, because it may be a feature I just don't know about.
where_did_the_extra_copy_come_from.jpg
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openBrain
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Re: where did this extra copy come from?

Post by openBrain »

One is the Fusion, the other is just the set of objects that are used inside the Fusion that are visible.
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Willem
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Re: where did this extra copy come from?

Post by Willem »

Please study the answers and advises you get. There are no changes on your file since the previous post. Another advice is to continue an existing post and do not start a new one for the same project.

I add a file with only a sketch out of the where_did_the_extra_copy_come_from.fcstd file. Can someone look to it and give an advice or this should be reported to Abdullah as a bug. There is a redundant dimension that is not detected by the Validate sketch option. The redundant dimension is long 128, 16 or 96 mm
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Bance
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Re: where did this extra copy come from?

Post by Bance »

There is something wrong in the sketch, it is over constrained. There is nothing locking Y position, but it cannot move in that direction.

I think it is a horizontal constraint between two points at the bottom of the sketch (constraint 16?) Should be an equality constraint maybe?
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Willem
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Re: where did this extra copy come from?

Post by Willem »

Constraint19 is the equality constraint, you can also say that this one is redundant. When you delete this constraint or one of the dimensions the sketch can be moved in X and Y direction. Because it is overconstrained it only moves in X direction. I think this should be determined by the sketch validation tool
chrisb
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Re: where did this extra copy come from?

Post by chrisb »

To be clear: It's not the sketch validation tool, which detects such things, it is the solver.

I remember that there were issues with the equality constraint, but I thought they were fixed. It is indeed possible to remove and recreate the equality, but it is not possible to replace it with another distance constraint at the right side.

Some observations:
There are 8 lines, which add 8x4 = 32 degrees of freedom (DOF)
The only constraints consuming more than 1 DOF are the coincidences
8 coincidences -> 16 DOF
23-8 Constraints consume 1 DOF -> 15 DOF

In total the constraints consume 31 DOF which is what the solver sees.

Adding a horizontal distance to one of the points, e.g. the lower left inner point makes it fully constraint - seemingly correct from the pure number of DOF consumed.
Alas, a horizontal distance to the lower left outer point makes it overconstraint.

I can also add to the original sketch a vertical distance to any of the points, which again shows it as fully constraint, again seemingly correct from the pure number of DOF consumed.

Conclusion: Create a bug report and assign it to Abdullah so it will not be forgotten.
A Sketcher Lecture with in-depth information is available in English, auf Deutsch, en français, en español.
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Shalmeneser
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Re: where did this extra copy come from?

Post by Shalmeneser »

If we kill one constraint, the sketch can move freely.
It's weird that over-constrain is not detected.

With the original sketch, the upper right point can be constraint with the origin, but not other points.
rek
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Re: where did this extra copy come from?

Post by rek »

Willem wrote: Thu Sep 16, 2021 12:35 pm Please study the answers and advises you get. There are no changes on your file since the previous post. Another advice is to continue an existing post and do not start a new one for the same project.

I add a file with only a sketch out of the where_did_the_extra_copy_come_from.fcstd file. Can someone look to it and give an advice or this should be reported to Abdullah as a bug. There is a redundant dimension that is not detected by the Validate sketch option. The redundant dimension is long 128, 16 or 96 mm
ok, will do. I just thought this was a different topic, i didn't want to turn a specific question into a general purpose help-me thread. But in the future, unless I have some objections I will follow this advice Willem. Thanks.
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Re: where did this extra copy come from?

Post by chrisb »

Abdullah, I see you are active here again - glad to see you back! Could you have a look at Willem's sketch extract: https://forum.freecadweb.org/viewtopic. ... ty#p533501 . Should we create a ticket?
Abdullah wrote:ping
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Re: where did this extra copy come from?

Post by abdullah »

chrisb wrote: Sat Sep 18, 2021 7:27 am Abdullah, I see you are active here again - glad to see you back! Could you have a look at Willem's sketch extract: https://forum.freecadweb.org/viewtopic. ... ty#p533501 . Should we create a ticket?
Abdullah wrote:ping
Yes, please. It is obviously redundant. It is worth investigating. Thanks!
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