Fillet command

Hi dear more ecperienced Users, I am still studying this excellent software, so I might be doing something wrong, but there is a phenomenon I cannot overcome: when creating fillet between a circle and a line, the result looks good at normal size, but when zooming in, it shows that the two lines are not connected. Does anyone have an idea what do I wrong? Thanks

Looks like same issue as https://forum.librecad.org/Draw-Chord-tp5723152p5723158.html (ie limit of GUI).

I think flywire has accidentally pasted a link meant for an other thread.
If I remember correctly LordofBikes once commented to a similar case that this phenomenon is caused by some screen rendering issue but can be ignored, as the geometrical calculation is OK.

You are right, I updated the original link. It is the post you recalled.

Thanks to everybody taking care of my problem.

This small inaccuracy would not be an issue, as it is not visible at normal size. However since the two lines do not intersect, I cannot use the Trim option, which is already a problem.

I will try to solve this issue on an other path: first trimming and then fillet.

Anyway, thanks again.

Trimming by tangent points is a fundamental issue here.

The proper way to address this issue would be introduction of topological entities here(like a vertex of tangential).

Using only geometry info is not enough. A tangent point by definition is when two intersection points are degenerate into one. Direct intersection calculation may give us 0, 1, or two intersections, depending on the tolerance level.

That being said, the initial fillet looks quite bad. Could you upload an example dxf, so I can verify the fillet feature works as expected.

To add topological entities is clearly a huge project, but we will see.

Dobro wrote

Thanks to everybody taking care of my problem.

This small inaccuracy would not be an issue, as it is not visible at normal size. However since the two lines do not intersect, I cannot use the Trim option, which is already a problem.

I will try to solve this issue on an other path: first trimming and then fillet.

Anyway, thanks again.

Thanks for the explanation, it sounds quite scientific, but I guess I could catch the core of it.

I've tried the other way as well, first trimming and then fillet, and the result is excellent.
Example_fillet.dxf

On the left there is the first attempt, where fillet is bad. On the right the second, where the line is uninterruptedly continuous.

So there's a solution for this problem, but one have to figure it out.

This is actually a long-overlooked bug in fillet. I can see the fillet arc is created properly, but trimming fails.

One workaround would be cutting the circle into an arc of 360 degrees (Tools > Modify > Divide and cut the whole circle by any point on it). Fillet works with arcs but not circles/ellipses. This also shows it's actually a bug.

I also found the fillet size GUI input is quite buggy. Need to be fixed.

This is not an issue of trimming, since trimming is not meant to handle tangential cases. For fillet, the trimming is by the closest point to the fillet arc center.

Dobro wrote

Thanks for the explanation, it sounds quite scientific, but I guess I could catch the core of it.

I've tried the other way as well, first trimming and then fillet, and the result is excellent.
Example_fillet.dxf

On the left there is the first attempt, where fillet is bad. On the right the second, where the line is uninterruptedly continuous.

So there's a solution for this problem, but one have to figure it out.

I pushed a fixed to the master branch:

1. handle trimming of circles for fillet;
2. Fixed fillet option GUI on memorizing user settings.

Dobro wrote

Thanks for the explanation, it sounds quite scientific, but I guess I could catch the core of it.

I've tried the other way as well, first trimming and then fillet, and the result is excellent.
Example_fillet.dxf

On the left there is the first attempt, where fillet is bad. On the right the second, where the line is uninterruptedly continuous.

So there's a solution for this problem, but one have to figure it out.

Thanks to everybody spending time on solving this problem.