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Splitting a mesh with an arc - Same question 10 years after ...

Alskaro
Contributor

Hello!

 

Everything is in the title .. I created a new post because I could not anwser to the old one (probably too old, what an irony).

 

How can I manage to achieve that ? Cutting someting with and arc or spline without to have a workaround with the magic hand tool.

 

On the previous post, some people said this method could not be used to cut slab or mesh because of the uncertainity of the intersection ..

Did someone at graphisoft found a solution after all this time ? I can magic wand an hatch with the curve I want and you pretend it's not possible to cut it ..

Maybe I missed something somewhere but I'm sure it's possible no ?

Well if someone have some idea about this topic ... 

 

Thank you for your answer,

have a nice day!

 

Alskaro_0-1753696136614.png

 

Operating system used: Windows 3001 FRA FULL

3 REPLIES 3
Barry Kelly
Moderator

Splitting along a line is easy as it just chooses one side or the other.

Splitting linear elements along an arc is also easy as it just finds the intersection of the reference line and the arc and splits it there.

The end of the wall is not curved.

 

Splitting an non-linear shape along an arc is much more difficult.

It can't just cut everything to one side.

 

BarryKelly_0-1753756653313.png

I am not sure a curved split would be an easy thing to program.

It might be possible, but it would be difficult.

 

Barry.

 

 

One of the forum moderators.
Versions 6.5 to 27
i7-10700 @ 2.9Ghz, 32GB ram, GeForce RTX 2060 (6GB), Windows 10
Lenovo Thinkpad - i7-1270P 2.20 GHz, 32GB RAM, Nvidia T550, Windows 11

Hello,

thank you for your message.

Sorry but I don't understand what you are talking about :

Alskaro_0-1753763811830.png

Could it not be done just with the same condition as for making the magic wand work ?(closed boundaries)

Have a nice day.

 

Splitting on a line (or arc) it is just choosing one side or the other.

For an arc, I think you will find it is creating an infinite length line perpendicular to the radius where it meets the reference line of the element to be split.

 

BarryKelly_5-1753774857120.png

 

So, for linear elements (lines, walls, beams) you are just dividing the reference line.

 

Forget my image in the first post (it should have said split, not cut).

Polygonal elements (slabs, meshes and fills) do not have reference lines to be split, which is probably why it does not work.

The split algorithm is looking for intersections of lines.

 

Take a simple 4 edge polyline on a slab.

How would it go about splitting this when the infinite edges all intersect each other.

 

BarryKelly_3-1753774483746.png

 

That is why it will choose just the edge you click on to split.

Curves will be even worse, as there would be almost an infinite number of splitting lines to consider.

 

Thinking about it more, if the subtract polygon method works, why not adapt that algorithm to leave the subtracted polygon, rather than delete it.

Of course that would only work with a closed figure, not a spline or polyline.

 

Barry.

 

 

One of the forum moderators.
Versions 6.5 to 27
i7-10700 @ 2.9Ghz, 32GB ram, GeForce RTX 2060 (6GB), Windows 10
Lenovo Thinkpad - i7-1270P 2.20 GHz, 32GB RAM, Nvidia T550, Windows 11

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