topic Re: twisted ribbon/object in Libraries & objects

twisted ribbon/object

Anonymous — Wed, 17 Nov 2004 06:33:28 GMT

Hello-
Please show me how this (attached) is done using GDL, I have posted this in 'Working in AC' section. I got a suggestion to bring it here. I have tried the mesh tool before, but didnt work. I would also like to know if I can manipulate/play with the surface of this object after creating it.
Please disregard materials.

Re: twisted ribbon/object

Anonymous — Wed, 17 Nov 2004 09:19:44 GMT

To do this in GDL will require the correct mathematics.

I haven't the time to noodle it out myself but it looks like a simple circular (sine) function should generate the values if the spiral is to be a regular one. Otherwise you will probably need additional parameters to introduce any distortions you want.

The SWEEP or TUBE statements are probably the best bet for the actual form. I recommend using a FOR-NEXT loop with a PUT statement to set up the coordinates and then use GET within the SWEEP or TUBE. There is some code similar to this in the manual.

Clever application of the graphical (or user) hotspots could make this into a very interesting part.

Re: twisted ribbon/object

Durval — Wed, 17 Nov 2004 15:46:08 GMT

Maybe this object may help you.
It was done as an exercise in one of our GDL classes here in São Paulo/Brazil.

Re: twisted ribbon/object

Anonymous — Wed, 17 Nov 2004 19:00:07 GMT

Geometric shapes are very easy in GDL. It is architecture that is difficult The GDL is actually quite simple - but a geometric background does help.

HTH !
Stuart 'prefers long variable names' James

!*** master variables ***

oRevolutions = 2
oSegmentAngle = 5 !=== in degrees
oCoilRadius = 5
oCoilLength = 50
oBandWidth = 5
oBandHeight = 2

!*** dependent variables ***

oAngle = 360 * oRevolutions
oStep = oAngle / (360/oSegmentAngle)
oXmultiplier = oCoilLength / oAngle

!*** put path ***

for i = 0 - oStep to oAngle + oStep step oStep

oX = i * oXmultiplier
oY = sin (i) * oCoilRadius
oZ = cos (i) * oCoilRadius
put oX, oY, oZ, i
next i

!*** draw path ***

tube 4, oAngle/oStep +2, 32+16+2+1,
-oBandWidth*0.5, -oBandHeight*0.5, 0,
oBandWidth*0.5, -oBandHeight*0.5, 0,
oBandWidth*0.5, oBandHeight*0.5, 0,
-oBandWidth*0.5, oBandHeight*0.5, 0,
get ((oAngle/oStep+2)*4)

end

Re: twisted ribbon/object

Anonymous — Thu, 18 Nov 2004 06:56:38 GMT

thanks guys,very helpfull

Durval, I would like to know how is it possible to make this ribbon start wide and end up thin or almost pointed. the width in the object is fixed all along.
I want it to look more like the one posted by Stuart, except for the thickness.

Stuart, please let me know how long it took you to do it?

and is that how you felt after doing it, turning around and around.

Re: twisted ribbon/object

Anonymous — Thu, 18 Nov 2004 13:02:53 GMT

Saif;

The 'one posted by Stuart' is an even thickness along the length. Here is a 'rough' variation which gives tapered ends. As long as you're happy with the geometry/maths this doesn't take long at all.

Note - it isn't an 'accurate' model but would suffice for many circumstances.... Now I'm curious! - just what are you trying to model???

HTH - Stuart

PS. DnC et al - yes I know that you should 'rot x,y,z' all along the helical path to do this 'properly' but I'd need a beer before coding that!

oRevolutions = 3
oSteps = 1000
oCoilRadius = 10
oCoilLength = 50
oBandMaxWidth = 2
oBandMaxHeight = 5
oHeight = oCoilLength/oSteps

roty 90

for j= -1 to oSteps+1

i = j/oSteps * 360 * oRevolutions
oBandWidth = oBandMaxWidth * sin(j/oSteps*180)+0.001
oBandHeight = oBandMaxHeight * sin(j/oSteps*180)+0.001

put oCoilRadius * cos(i) - oBandWidth * cos (i) + oBandHeight * sin (i),
oCoilRadius * sin(i) - oBandWidth * sin (i) - oBandHeight * cos (i), oHeight,
oCoilRadius * cos(i) + oBandWidth * cos (i) + oBandHeight * sin (i),
oCoilRadius * sin(i) + oBandWidth * sin (i) - oBandHeight * cos (i), oHeight,
oCoilRadius * cos(i) + oBandWidth * cos (i) - oBandHeight * sin (i),
oCoilRadius * sin(i) + oBandWidth * sin (i) + oBandHeight * cos (i), oHeight,
oCoilRadius * cos(i) - oBandWidth * cos (i) - oBandHeight * sin (i),
oCoilRadius * sin(i) - oBandWidth * sin (i) + oBandHeight * cos (i), oHeight,
oCoilRadius * cos(i) - oBandWidth * cos (i) + oBandHeight * sin (i),
oCoilRadius * sin(i) - oBandWidth * sin (i) - oBandHeight * cos (i), oHeight

if j>=0 and j<=oSteps then
ruled 5, 51,
get(2), get(1)*0,
get(2), get(1)*0,
get(2), get(1)*0,
get(2), get(1)*0,
get(2), get(1)*0,
use(15)
addz oHeight
endif

next j
del top[/size]

Re: twisted ribbon/object

Anonymous — Thu, 18 Nov 2004 15:26:49 GMT

saif wrote:
Stuart, please let me know how long it took you to do it?

Saif;

The first one took about 4 minutes (+1 minute to render). The second example took 6:30 minutes (yes I timed it! + 2 minutes to render).

But if 3d geometry isn't your cup of tea then it could take a lot lot longer...

- Stuart

Re: twisted ribbon/object

Anonymous — Thu, 18 Nov 2004 17:03:00 GMT

Having had a beer (:)) here's a 'better' solution...

oSe = 0300 !=== no. of segments
oCr = 0005 !=== helix diameter
oBw = 0002 !=== width of band
oAn = 1500 !=== total revolved angle
oLe = 0050 !=== total length

for j=-1 to 1 step 2 : for i=0 to oAn step oAn/oSe
put oCr*cos(i)+j*oBw*cos(i)*sin(i/oAn*180)
put oCr*sin(i)+j*oBW*sin(i)*sin (i/oAn*180)
put i/oAN*oLe
next i : next j

for i=0 to oAn step oAn : for j=0 to 1
put oCr*cos(i) : put oCR*sin(i) : put i/oAN*oLe
next j : next i

coons (nsp-12)/6, 2, 60, get (nsp)[/size]

Re: twisted ribbon/object

Durval — Thu, 18 Nov 2004 17:28:21 GMT

StuartJames wrote:
Having had a beer (:)) here's a 'better' solution...

WOW! Where can I find one of these beers?
Maybe it alows me to understand your elegant piece of code...
Up to the ruled script I was following your mathematics.
But this coons solution made me a bit lost. Could you give some clue on how you worked out these geometric equations?

Re: twisted ribbon/object

Karl Ottenstein — Thu, 18 Nov 2004 18:07:10 GMT

Durval wrote:
WOW! Where can I find one of these beers?
Maybe it alows me to understand your elegant piece of code...
Up to the ruled script I was following your mathematics.
But this coons solution made me a bit lost. Could you give some clue on how you worked out these geometric equations?

Exactly. Give us a bit of a lesson here, Stuart! Or tell us which beer!

Karl

Re: twisted ribbon/object

Aussie John — Fri, 19 Nov 2004 07:28:39 GMT

coons is a mystery to me

Re: twisted ribbon/object

Anonymous — Fri, 19 Nov 2004 13:59:38 GMT

You can try the internationally famous 'Efes Pilsen' brand !

I've started a new thread over at Coons 101. Please make contributions to the usual PayPal account.

- Stuart 'just pleased for an excuse to get his post no.s up' James

Re: twisted ribbon/object

Anonymous — Mon, 22 Nov 2004 04:57:15 GMT

shukran all,

Stuart I'm trying to model a complex sculpture in which the twisted shape is only a part of it. When I finish it sometime I will post it.

thanks again

Re: twisted ribbon/object

Ignacio Azpiazu — Mon, 22 Nov 2004 07:16:14 GMT

Karl wrote:
Or tell us which beer!

It is definitely not the beer. Stuart's profile portrait leaves no doubt as to the fact that he was born for these helical stuff things.

Re: twisted ribbon/object

Dwight — Mon, 22 Nov 2004 10:52:00 GMT

Let me add my admiration.
This is ballet.

Re: twisted ribbon/object

Anonymous — Sun, 02 Oct 2011 17:06:22 GMT

StuartJames wrote:
Geometric shapes are very easy in GDL. It is architecture that is difficult The GDL is actually quite simple - but a geometric background does help.

HTH !
Stuart 'prefers long variable names' James

!*** master variables ***

oRevolutions = 2
oSegmentAngle = 5 !=== in degrees
oCoilRadius = 5
oCoilLength = 50
oBandWidth = 5
oBandHeight = 2

!*** dependent variables ***

oAngle = 360 * oRevolutions
oStep = oAngle / (360/oSegmentAngle)
oXmultiplier = oCoilLength / oAngle

!*** put path ***

for i = 0 - oStep to oAngle + oStep step oStep

oX = i * oXmultiplier
oY = sin (i) * oCoilRadius
oZ = cos (i) * oCoilRadius
put oX, oY, oZ, i
next i

!*** draw path ***

tube 4, oAngle/oStep +2, 32+16+2+1,
-oBandWidth*0.5, -oBandHeight*0.5, 0,
oBandWidth*0.5, -oBandHeight*0.5, 0,
oBandWidth*0.5, oBandHeight*0.5, 0,
-oBandWidth*0.5, oBandHeight*0.5, 0,
get ((oAngle/oStep+2)*4)

end

hello, i'm newbie
a question:

and if the path of the ribbon is not straight but it's a circumference and the diameter of the imaginary "tube" (the diameter's size of the ribbon) is not constant but it decrease gradually (the ribbon grow and grow), how should I modify the code?

tnx