Does anyone have a tip on how to cut a circle with two tangents so that only the tangents and the circle segment between the two segments remains (the left-hand circle segment in the drawing below), without having to draw extra auxiliary lines?
You're absolutely right. I should read twice and reply once.
I have a question. How do you identify a tangent point? Surely you need a line from an external point to define the tangents. Are these auxiliary lines?
Join the ends of these external tangents and use the resulting triangle to cut the circle.
I'm missing something here. A tangent is a line intersecting the curve at one point only. What do you mean by auxiliary lines? Why do you want to avoid them? My "cutting" path is part of the geometry whether you draw it or not. In fact, Inkscape deletes it when you apply the cut operation. I just left a copy on the page for clarity.
As Tyler hinted, there are algebraic and trigonometric methods to calculate the exact coordinates of tangent points. If that's what you need you'll need some programming, or else look beyond Inkscape to a dedicated geometry program. Maybe something like this. https://www.geogebra.org/
and the circle segment between the two segmentstangents 🤭 remains (the left-hand circle segment in the drawing below),
without having to draw extra auxiliary lines [the red one]?
In other, more general words: is it possible to cut a closed shape open, for example a circle, at the point where a line, for example a tangent to the circle, touches the circle?
Inkscape is a graphic design application, not a CAD application and not a geometry application. Snapping to tangents is subject to round-off errors so you can't assume that you found an exact solution. The tangent line is close to correct, but may in fact intersect at two points or none. You might be able to cut the circle at the intersection, but you can't rely on it. Drawing the auxiliary line removes this ambiguity. There's always an intersection point to be found, even if this point is likewise an approximate solution.
The tangent line is close to correct, but may in fact intersect at two points or none.
No. If a tangent line is snapped to a circle, while it might not be a mathematically exact tangent, its endpoint is snapped *absolutely* correct to the circle's path, exactly as any other snapped line.
Let's forget about the original question and about the tangent line:
Is there any path function that DIRECTLY cuts a closed shape open, for example a circle, at the point where a line is snapped to the shape?
Cutting curves with tangents is not reliable. Likewise cutting with normals. Cutting with extended normals works every time. It seems that single-point intersections sometimes fall outside inkscape's detection tolerance. I think this could be classed as a bug.
My testing was not extensive. I drew a random open curve, two tangents, their two normals, then [Path > Cut Path]. I haven't tested closed shapes, tangent angles, other curvatures, etc.
Yes, it does not seem to work properly or reliably. But since the Cut command removes the line from the drawing anyway, it would not help in my case even if it worked reliably, because I'd want to keep the tangent lines.
So I guess the easiest and best still is to use an auxiliary line, which then is automatically removed by the Cut command.
I still don't understand what the starting point of this construct is. Start with a circle - then the tangents or the other way around. In the first case you can simply extend the lines until they meet ans snap - then combine and join them and the path effect Corners inserts a perfect circle segment:
Is this what you are eventually looking for? (How I did it is immaterial). Your explanation, of what you wanted, lacked clarity or example. (At least I was a little confused)
So I did a quick recording for this problem and I think I got what you need. If you have questions about what/how I things in the attached video, feel free to ask.
If you're looking for the smaller arc AB in post #1, or the green arc in post #8, you can enable tangential snapping and try the method in the video. However, you need to know the position of the point where both tangents intersect.
I feel like a step could be reduced in my solution as I think it was possible to snap Ellipse nodes to Path nodes. But I couldn't find any snapping settings regarding it, so I might be misremebering. If anyone else remembers, please let me know.
Is everyone trying to solve the question, which is not even open anymore, by using the absolutely most complicated way possible?
Ich kann seit Wochen eigentlich nur noch den Kopf schütteln über diesen Thread hier 🤦
Everyone who feels wanting to contribute something here should take about 15 minutes to read #8 and then think about it again for 15 minutes
As I fear that this will still not be enough, I shall repeat the question another time and believe that no more answers will be forthcoming other than "No".
Is it possible to cut a closed shape open, for example a circle, at the point where a line, for example a tangent to the circle, touches the circle?
…IN A SINGLE COMMAND AND WHILE KEEPING BOTH THE CIRCLE AND THE LINE FOR THE SAKE OF THE ALMIGHTY
@tukykarmakar I like it. I did nothing at all like that. I drew a circle, extended a line from the center, rotated 90 degrees and flipped horizontal.... etc etc, but worked. I found this discussion interesting. This made me hve a look at various Inkscape uses and was fun. I even used QCAD and exported SVG - worked a charm. Both our solutions seems to have produced a similar result.
It would have been nice to see what the end result was expected other than some description of an arbitrary scenario in broken English.
Beyond the Basics How to cut a circle at two tangents?
Inkscape.org
Does anyone have a tip on how to cut a circle with two tangents so that only the tangents and the circle segment between the two segments remains (the left-hand circle segment in the drawing below), without having to draw extra auxiliary lines?
Turn on snapping and select [Nodes > Tangential lines] to find tangent points using the Bezier Pen [b].
You didn't read any farther than "circle" and "tangent", did you?
You're absolutely right. I should read twice and reply once.
I have a question. How do you identify a tangent point? Surely you need a line from an external point to define the tangents. Are these auxiliary lines?
Join the ends of these external tangents and use the resulting triangle to cut the circle.
Argh
You seek the trig formula?
I'm missing something here. A tangent is a line intersecting the curve at one point only. What do you mean by auxiliary lines? Why do you want to avoid them? My "cutting" path is part of the geometry whether you draw it or not. In fact, Inkscape deletes it when you apply the cut operation. I just left a copy on the page for clarity.
As Tyler hinted, there are algebraic and trigonometric methods to calculate the exact coordinates of tangent points. If that's what you need you'll need some programming, or else look beyond Inkscape to a dedicated geometry program. Maybe something like this. https://www.geogebra.org/
Sorry, a typo.
In other, more general words: is it possible to cut a closed shape open, for example a circle, at the point where a line, for example a tangent to the circle, touches the circle?
No.
Inkscape is a graphic design application, not a CAD application and not a geometry application. Snapping to tangents is subject to round-off errors so you can't assume that you found an exact solution. The tangent line is close to correct, but may in fact intersect at two points or none. You might be able to cut the circle at the intersection, but you can't rely on it. Drawing the auxiliary line removes this ambiguity. There's always an intersection point to be found, even if this point is likewise an approximate solution.
No. If a tangent line is snapped to a circle, while it might not be a mathematically exact tangent, its endpoint is snapped *absolutely* correct to the circle's path, exactly as any other snapped line.
Let's forget about the original question and about the tangent line:
Is there any path function that DIRECTLY cuts a closed shape open, for example a circle, at the point where a line is snapped to the shape?
I've done some testing.
Cutting curves with tangents is not reliable. Likewise cutting with normals. Cutting with extended normals works every time. It seems that single-point intersections sometimes fall outside inkscape's detection tolerance. I think this could be classed as a bug.
Interesting. Did you try cutting a closed shape, or only an open shape, i.e. a line?
My testing was not extensive. I drew a random open curve, two tangents, their two normals, then [Path > Cut Path]. I haven't tested closed shapes, tangent angles, other curvatures, etc.
Yes, it does not seem to work properly or reliably. But since the Cut command removes the line from the drawing anyway, it would not help in my case even if it worked reliably, because I'd want to keep the tangent lines.
So I guess the easiest and best still is to use an auxiliary line, which then is automatically removed by the Cut command.
I still don't understand what the starting point of this construct is. Start with a circle - then the tangents or the other way around.
In the first case you can simply extend the lines until they meet ans snap - then combine and join them and the path effect Corners inserts a perfect circle segment:
This looks like a few more clicks to achieve the same as using that one auxiliary (red) line as discussed.
The OP OTOH was about whether it is possible WITHOUT additional constructs. Which doesn't seem to be the case.
Still don´t get the use case.
As already noted a few times, this is not about what tangents are or how to construct them.
I believe the case can be closed.
Is this what you are eventually looking for? (How I did it is immaterial). Your explanation, of what you wanted, lacked clarity or example. (At least I was a little confused)
The question is in #8, and the answer is no, it's not possible 💁♂️
So I did a quick recording for this problem and I think I got what you need. If you have questions about what/how I things in the attached video, feel free to ask.
If you're looking for the smaller arc AB in post #1, or the green arc in post #8, you can enable tangential snapping and try the method in the video. However, you need to know the position of the point where both tangents intersect.
I feel like a step could be reduced in my solution as I think it was possible to snap Ellipse nodes to Path nodes. But I couldn't find any snapping settings regarding it, so I might be misremebering. If anyone else remembers, please let me know.
Sorry, but what the *** are you doing there?
Is everyone trying to solve the question, which is not even open anymore, by using the absolutely most complicated way possible?
Ich kann seit Wochen eigentlich nur noch den Kopf schütteln über diesen Thread hier 🤦
Everyone who feels wanting to contribute something here should take about 15 minutes to read #8 and then think about it again for 15 minutes
As I fear that this will still not be enough, I shall repeat the question another time and believe that no more answers will be forthcoming other than "No".
Is it possible to cut a closed shape open, for example a circle, at the point where a line, for example a tangent to the circle, touches the circle?
…IN A SINGLE COMMAND AND WHILE KEEPING BOTH THE CIRCLE AND THE LINE FOR THE SAKE OF THE ALMIGHTY
@tukykarmakar I like it. I did nothing at all like that. I drew a circle, extended a line from the center, rotated 90 degrees and flipped horizontal.... etc etc, but worked. I found this discussion interesting. This made me hve a look at various Inkscape uses and was fun. I even used QCAD and exported SVG - worked a charm. Both our solutions seems to have produced a similar result.
It would have been nice to see what the end result was expected other than some description of an arbitrary scenario in broken English.
Cheers tukykarmakar.
We'd better close this topic, in my opinion.
@DavidP : I'm not sure that's the best way to get help and thank people who spent time to help you.
Ok, I'll lock it. (But I find it entertaining. 😈)
In closing, I'll point our readers to CAD programs like LibreCad which have functions that can modify geometry between or up-to intersecting geometry.
Inkscape may not have many of these tools, but who knows what the future brings?