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Cloud Hidden

Wrapping a surface

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One object is a cylinder. I turn it into a shell of whatever thickness. I want cut a big hole in that shell. The hole has a specific shape. Let's pick a star pattern. Now if I draw the start pattern flat, when I project it onto the ball, the star pattern will be distorted (in 3D) because of the curve to the cylinder. For example, if the cylinder is 10 units diameter and the star is 10 units across, with projecting the star, it'd cut through the full width of the cylinder...not what I want. But if the shape is wrapped around the cylinder, it'd only cut through 1/3 of its circumference.

Which combo of tools will let me cut the star shape in the cylinder accurately?

Thanks.

[ 03-15-2005, 02:19 PM: Message edited by: Cloud Hidden ]

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I spent more time searching, and found the same question posted two years ago (by ME, no less!) with the answer that it cannot be done. Unless something's changed, that seems to be where it sits.

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I assune you want to cut the cylinder at right angles to the surface each time. This will require you to 'kern' the basic shape so that it will cut correctly.

Try this and see if it will work:

- model your pipe in Top/Plan View

- draw your 2D shape in Front View and turn it into a 3D polygon.

- Distort the shape horizontally by Assymetrically Rescaling the object (Factor = arc length / actual width)

- Convert the 3D polygon into a NurB

- Place a 3D loci at the centre of the pipe and adjust its height so that it is on the CL of the shape

- Place the Nurb shape in the location required to give the correct 'cut'.

- Loft between the Nurb shape and the 3D loci to form the cutting object

- Solid Subtract the cutting object from the cylinder.

The only bit I am unsure of is the scaling factor - basically you want the radial lines from the horizontal extremities of the object to intersect with the ends of the 'shape'.

Good luck

I have just realised that won't in fact work because as you work around the shape the shape tapers in the Z direction.

Anybody else have any thoughts?

[ 03-16-2005, 12:35 AM: Message edited by: mike m oz ]

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This was exactly one of the things I had tried, figuring it might be close enough. Unfortunately the solid subtract gave me a "we can't perform this operation" error or whatever it was.

Thanks for thinking about it though!

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I played around and managed to get a result in the end - but a distorted one.

What I did was:

- Draw the required 2D shape and then copy it.

- I then assymetrically distorted the original polygon by a factor of 0.5 in the X direction.

- I then Pasted in Place a copy of the 2D shape and then assymetrically distorted this polygon by a factor of 1.5 in the X direction.

- I then did a Multiple Extrude which gave me a cutting object which varies only in the X direction.

- By placing the origin of this cutting object coincident with the centre of the tube I ensured that the cutting planes were at 90? to the cylinder surface (or so I thought)

- I then Solid Subtracted this cutting object from the cylinder.

The result unfortunately does not give the correct shape.

What you really need is the ability to curve a 3D polygon to a specific radius. Then by Shelling it you could create a 'cutting object' which would be correct.

You might have to look outside of VectorWorks for the capability of doing this. Perhaps Cheetah3D might be an option. homepage.mac.com/mwengenm/Cheetah3D/

Having created the object you could then import it back into VW.

[ 03-16-2005, 08:34 PM: Message edited by: mike m oz ]

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I thought this would be a problem that people would be challenged by and itching to get into and solve

There must be someone else out there with an understanding of the maths and some thoughts on how to do it.

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Cloud Hidden - there is a Warp Modifier in Cheetah 3D which looks as if it will do what you want.

It will also wrap text to a curve so may be a way of solving the problem previously posted by others on how to do this.

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quote:

Originally posted by mike m oz:

I thought this would be a problem that people would be challenged by and itching to get into and solve

There must be someone else out there with an understanding of the maths and some thoughts on how to do it.

In Julian Carr's "Pro Pack" for VW9 there was a VectorScript based 3D text function which would wrap extruded text around a cylinder.

So, notionally it should be do-able. -Easy for me to say ;-D

Personally, I think I would be stuck doing it "manualy" by projecting lines. Much like doing a Development in reverse.

I must say, though, that I don't think I've done a development since the heady days of 1972 Tech Drawing solid geometry classes. I might have to think about it a bit. :-D

All of that piffle aside, Wrapping, unwrapping,Warping (etc) functionality in VW would be a significant 3D enhancement.

N.

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quote:

Originally posted by mike m oz:

just fill in a few of the gaps and we would have a great modelling package.

Hey Mike,

"just fill in a few of the gaps" is easy for us to say ;-)

but the task in question is obviously beyond either of us :-D

VW12 perhaps?

cheers,

N

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Here?s a method, there are shortcuts but I'm hoping this is the best way to follow first time through:

1) Create your cylinder. I drew a circle of radius 5, offset another inside it, clipped surface and extruded.

2) We need to determine the distorted dimensions of a flat star so that when projected it will not be distorted.

a) Find the angle of an arc whose length is 10 and whose radius is 5

Theta = L/tanr =10/tan5 =114.3 degrees

b) Draw an arc of 114.3 degrees with a radius of 5 so that it is symmetric about the x axis (starting 57.15 degrees above and ending 57.15 below).

c) Draw lines from the center of the arc to its endpoints.

d) Draw a vertical line tangent to the arc.

e) Connect the two c) lines and the d) line, making a triangle.

f) Determine the length of the d) line ?I get 15.5.

3) Draw the 2D star, group it, distort the x value from 10 to 15.5.

4) Put a loci in the center of the star, multiple extrude the two to the radius of the cylinder; 5.

5) Place the locus point of the pyramid-like star at the center of the cylinder, subtract solids.

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Its not perfect as the star is uniformly distorted in width whereas it should become progressively longer toward the extremities, but if you're not dimensioning off it it may be close enough.

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Years ago, I used to be able to do this in Adobe Dimensions - a programme that has since been discontinued. The cool thing was, that I could wrap any 2D vector graphics around any 3D shape. I hope, that a future VW-Designer package will include this feature.

Cloud, I am sure you can work this out 'manually' as long as the shapes are no more complex than a star and a cylinder. But it is not cool, that you would have to.

A somewhat inacurate workaround is to texture-wrap a black star on white background in high resolution, using the cylinder wrap. Render it and trace the rendered image to get the distorted shape.

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I think the way to achieve this in VectorWorks may be implementing a feature like "Replace Surface". What you do is you select the planar star and ask the spplication to replace it by a cylindrical surface. I am thinking of adding it for a coming release.

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>I am thinking of adding it for a coming release.

That would be wonderful!

And thanks to the other people who have looked at this and offered workarounds.

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Just a thought...

Extrude the star so that it has a length sufficiently long enough to go through the cylinder.

Make a duplicate of the cylinder and turn it into a shell object.

By taking the intersection of these two objects you should be left with a shape that is essentially all of the curves where the star has intersected the cylinder.

From there you could make a solid out of the shape (a new extrude) that has the correct curvature, and subtract it from the original cylinder.

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On 4/16/2005 at 6:04 AM, grant_PD said:

Just a thought...

Extrude the star so that it has a length sufficiently long enough to go through the cylinder.

Make a duplicate of the cylinder and turn it into a shell object.

By taking the intersection of these two objects you should be left with a shape that is essentially all of the curves where the star has intersected the cylinder.

From there you could make a solid out of the shape (a new extrude) that has the correct curvature, and subtract it from the original cylinder.

 

Isn't that just the same as projecting the star onto the cylinder? The form of the hole (the star) will be distorted when the surface is unwrapped flat. 

 

This thread was started about 16 years ago. I'm wondering if there has been any development since then?

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On 3/24/2021 at 3:41 PM, grant_PD said:

Deform tool!

 

Thanks @grant_PD! For some reason I didn't realize that you can do an even circle with the deform tool. Perfect solution for wrapping a cylinder! Doesn't solve wrapping on ellipsoidal or wavelike forms though, but happily I don't need that for now...

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