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Everything about using Libraries and Library Parts - Doors/Windows/Objects/Stairs etc. (Example: How can I display a Transom above my Door?)

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By Bruce
I'm developing a bent spring object, using the TUBE command. I've got the maths working, but unfortunately, the TUBE command puts small creases in the profile as it starts to go over the bend. You will also see some large twists near the apex.

I've have tried playing with the angle parameter, but it has little effect.

I've conferred with some colleagues, who are confident this is either a bug, or beyond the capacity of TUBE to deal with.

Any ideas?
spring.jpg (152.29 KiB) Viewed 1066 times
By DGSketcher
I'm not an advanced GDL coder, but if this is one continuous tube around a centre of rotation then perhaps you might get around the graphic problems by creating the end spirals and then infill with a single 360 degree spiral?

This might also help if you haven't already got it... ... index.html

I still refer to it on a regular basis.

Just checked DNC's book and he does make reference to problems with rendering TUBE and seems to favour using bPrism for this type of object.
By Pertti Pääsky
Hi, you could examine the geometrics by switching the wireframe on. The tube section's orientation needs to be calculated and in some cases knots can appear. By splitting the tube into suitable pieces this problem can be avoided.
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By Bruce
Thanks all. I've had a look at these various options, but to no avail. Splitting into smaller segments seems to be the only way...which still creases a bit.

Does anyone from Graphisoft have any input?
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By Erwin Edel
It seems that the circle segments that are connected to form the tube twist around the axis, causing the creases.

Maybe try coding one with a square or triangle polygon to fix the rotation around the axis that happens, than switch back to the circulare polygon.

If you set RESOL to 3 you can see it happening more clearly. The twisting that is.
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By Moonlight
Hi every one,

Have anyone of you found a way to stop the profile's rotation ?

Or have abyone found the way to calculate that rotation ?
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By Bruce
Not to my knowledge - this is an inherent problem with the TUBE command.

It's almost irrelevant, but I tried the same coding (well, logic) using Ruby inside SketchUP, and the FollowMe command, and no twisting. So it's definitely unique to the TUBE GDL.