Sketch symmetry and constraints

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tomkcook
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Joined: Wed Jul 20, 2016 3:39 pm

Sketch symmetry and constraints

Post by tomkcook » Tue Nov 29, 2016 10:41 am

I have a sketch which is built along one side of the Y axis, with end points constrained to that axis. The sketch is fully constrained.

I select all elements of the sketch, then select the Y axis. Then I select Sketch -> Sketcher Tools -> Symmetry. The geometry is correctly mirrored across the Y axis, but the constraints are not - my sketch now has 14 degrees of freedom. It looks as though distance, horizontal, vertical and coincident constraints are copied to the mirrored geometry but angle constraints are not.

I've tried this on both 0.16 and 0.17 build 9082. Am I doing something wrong? Is this how it's meant to work?
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NormandC
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Re: Sketch symmetry and constraints

Post by NormandC » Wed Nov 30, 2016 5:53 am

tomkcook wrote:Is this how it's meant to work?
I'm getting the same result here so I'd say yes. Sometimes some tools are not fully implemented or have limitations.

If you want, you could create a bug report on the bug tracker. To the left of the Search box at the top is a bug icon, click on it to go to the bug tracker.
wanders
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Re: Sketch symmetry and constraints

Post by wanders » Fri Mar 02, 2018 2:44 pm

I'm seeing the exact same issues in 13331, more than a year later.

What is needed, I think, is to be able to symmetrically reflect a clone (complete with constaints) across an axis or line, rather than copy the elements. By the way, in my opinion, cloning should be the default way to replicate sketch elements in parametric CAD - copy should be the secondary choice.

Who is the lead developer for sketcher? Sketcher really has an interesting, unique and fun-to-use constraint system, which I really like. There is still a lot of work to do on the sketcher, however.
chrisb
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Re: Sketch symmetry and constraints

Post by chrisb » Fri Mar 02, 2018 5:20 pm

wanders wrote:
Fri Mar 02, 2018 2:44 pm
Who is the lead developer for sketcher? Sketcher really has an interesting, unique and fun-to-use constraint system, which I really like. There is still a lot of work to do on the sketcher, however.
Hi wanders, welcome to the FreeCAD forum. I think Abdullah is currently doing the most if not all work in Sketcher. He sure can need some help.
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MIKHAYLOV_YV
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Re: Sketch symmetry and constraints

Post by MIKHAYLOV_YV » Wed Jan 15, 2020 11:39 pm

I'm watching FreeCad lesson # 1. And I see a problem with symmetry. I tried to send a different choice. The error "Recompute failed" remains ((
The sketch is updated correctly.

Do i need to create issue on github?

Image
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wandererfan
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Re: Sketch symmetry and constraints

Post by wandererfan » Thu Jan 16, 2020 12:38 am

MIKHAYLOV_YV wrote:
Wed Jan 15, 2020 11:39 pm
Do i need to create issue on github?
I don't think so. What happens if you delete constraints 5 & 8?
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MIKHAYLOV_YV
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Re: Sketch symmetry and constraints

Post by MIKHAYLOV_YV » Thu Jan 16, 2020 4:33 am

Then the sketch will be destroyed. Try to do the same for yourself. Maybe I Have a bad build FreeCad
chrisb
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Re: Sketch symmetry and constraints

Post by chrisb » Thu Jan 16, 2020 10:44 am

MIKHAYLOV_YV wrote:
Wed Jan 15, 2020 11:39 pm
I'm watching FreeCad lesson # 1. And I see a problem with symmetry.
I don't know where you found it, but this lesson seems to be very old. The error concerning symmetry was already present then, alas, it was not reported. Nevertheless it frequently lead to errors in later steps. This was the original reason to collect some in-depth information about sketcher (if you are interested: https://owncloud.gwdg.de/index.php/s/HS ... I/download).

If the ketch gets destroyed when you remove the redundant horizontal and vertical constraints, then you have probably added erroneous constraints, after there was an error signaled from the solver. Always keep an eye on the solver messages, and fix any error before you continue to add more constraints.
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bejant
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Re: Sketch symmetry and constraints

Post by bejant » Thu Jan 16, 2020 2:16 pm

MIKHAYLOV_YV wrote:
Thu Jan 16, 2020 4:33 am
Then the sketch will be destroyed.
I don't think so. From your image it looks like Constraint5 is the Horizontal Constraint on the top line segment and Constraint8 is the Vertical Constraint on the left line segment, so the way that the Symmetry Constraints are applied makes these become Redundant.

But in your Sketch I'll suggest you keep Constraints 5 and 8, delete the two Symmetry Constraints (Constraints 9 and 10), then apply one Coincident a single Symmetry Constraint between two diagonal corners of the square and the Origin.

blue and strike through = edit
Last edited by bejant on Thu Jan 16, 2020 3:19 pm, edited 1 time in total.
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wandererfan
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Re: Sketch symmetry and constraints

Post by wandererfan » Thu Jan 16, 2020 2:35 pm

bejant wrote:
Thu Jan 16, 2020 2:16 pm
then apply one Coincident Constraint between two diagonal corners of the square and the Origin.
Should be Symmetry Constraint?
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