I am exploring various algorithms to bend shapes in the context of my plugin FredoBend.
Starting with the rectangular shape on the left, here are 2 ways to bend it at 180 degrees:
They look the same, but there are slight differences.
Looking into the attached model file, which one would consider correct: A or B?
Bend 180 - Question.skp (195.8 KB)
Hi Fredo,
B - keeps the initial width of 7.3509 m and also creates quads on the horizontal faces (top/bottom), better for texturing.
Thanks. But, just ignore the question of soften and coplanar edges. This is something independent of the bending and Iâll provide options to keep quads or not.
My question is related to assessing which algorithm is closer to the real-world situation.
kendi dilimdi yazıyorum , metelurjik açıdanmı deÄerlendircez , gerçek bir bĂŒkmeden mi bahsediyoruz özellikleri çok benzer , en önemli Ćey line lar kopuk , gerçek bir bĂŒkĂŒlmeden bahsediyorsak , malzemenin baĆ kısımlarında çekme olmalı , burada yok , imalat için simĂŒlasyonda kullanacaksam , gerçek bĂŒkme olmalı , seni araçlarında benzer özellikleri sunan bir araç vardı öyle hatırlıyorum , nasıl inceleyeceÄimizin konusunu tam olarak belirtirsen , talep fikirlerimiz olur . Saygılar
You would need to give an example of how a shape is stretched âat the endsâ in metalworks. Is there any formula?
Look up âThinningâ and âK-Factorâ.
The width of the rectangular shape is 7.3509 m.
So, this picture may help to decide what should be the result:
And the picture below shows the bending at 360 degrees with 3 segments in cases A and B.
Bend 180 - Question.skp (221.5 KB)
I tested in Blender with a Bend modifier. The result is that of variant B, the one that preserves the original width at all inflection points. But in some situations, option A is also good, if it keeps the original width along the entire length (as an offset for the side edges).
Reality - it seems to preserve the width (offset) - option A
on instinct, Iâd say A.
because I donât bend metal, but Iâve bent my share of cardboard, plywood and other thinks like that by scoring one side.
what matters there is the thickness of the board. solution A retains the thickness.
the 3 sided example is good, if I want to make such a shape with a 7,3509 board, then yeah, A is correct.
B is a different case, itâs bending the material so that no thickness is greater than the initial material. it might make sense in term of maths, as you âsliceâ the initial model and the slice geometry it retained.
what hurts my brain is that A is more correct, it retains the thickness of the element.
but B works with the same logic as Sketchup circles and arcs, with only the endpoints being correct.
A seems more correct because:
I would have thought that A is closer to a FollowMe, but I am also lost with how FollowMe works.
Below I took a square 10mx10m and follow it along a half-circle with 24 segments and a 3-edge rectangular curve.
I am lost at the resultsâŠ!
Bend 180 - Question.skp (201.2 KB)
In the second video (Bend 3c), the vertical sides of the shape are not kept vertical. Is there something different coming from Blender?
At first I thought it was necessary to have quad geometry, but thatâs not the case. Iâll have to search and see if I can find an answer to this problem, to keep those faces like in SketchUp.
I think I found an explanation about the Follow Me and Offsetting differences between an arc of circle and a polygon.
In the attached model, I draw a circle and a polygon, both with a radius of 50 m and 12 segments. So, geometrically, the shapes are identical.
Then, I use the offset tool by typing 10 m in the VCB.
Now the surprising result:
CONCLUSION: It does matter whether your curve is a true circle or arc of circle versus a polygon.
Note that if you just explode the circle, then the behavior is like a polygon.
doesnât surprise me, you draw the circle / arc based on its radius, between center and vertices.
but polygon can be drawn according to inside / outside circles, ie you can draw one based on the width between its sides, not vertices.
and from your test with follow me, it seems prioritises vertices only with true arcs and circles.
so a solution would be to explode into a polygon prior to the operation then ? if you want coherence with all the other tools ?
In the case of FredoBend Circular or True Bend, the circle is implicit and the user should be given the choice.
TrueBend, which is Algorithm B in the post above apparently chose to use a True Circle algorithm.
For FredoBend Circular, I was thinking of using algorithm A, but now that I understand better what Sketchup does with Offset and FollowMe tools, I will offer the choice between A and B.
Note that the true circle algorithm is not really appropriate to cases where you have few segments, but at least it is consistent.
My knowledge of tensile strength is weak.
I was very surprised
I would provide both as options and then select one as the default behavior but the question is which one should be default.
The question is also how to give a meaningful name to the two options�
