Is there any way to get a spiral or helical object without merging (or
blobbing) a bunch of primitives? And is there a way to get a helical
texture without an image map? I know there's a spiral pattern, but no
helical one...

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You could approximate a helix with triangles, but I don't think a true
helix is possible without the isosurface patch.
And I think the spiral pattern will do what you want, it isn't really a
spiral but a kind of helix.

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Think Larry's son  : )  means a spiral texture lacking in a center or
continuation beyond a certain radius.  Try a 'wood' 'texture_map' with
a clear (or otherwise plain) pigment as both beginning and end
indecies, the 'spiral1 2'texture at index 0.25 and 0.75, for example.
 Far as the object itself goes perhaps torus slices, rotated and
translated. Well you did ask  ; )

Bob

Chris Huff <Chr### [at] compuservecom> wrote in message
news:37D0430E.AA158CC2@compuserve.com...
> You could approximate a helix with triangles, but I don't think a
true
> helix is possible without the isosurface patch.
> And I think the spiral pattern will do what you want, it isn't
really a
> spiral but a kind of helix.
>

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Bob Hughes wrote:

> Think Larry's son  : )  means a spiral texture lacking in a center or
> continuation beyond a certain radius.  Try a 'wood' 'texture_map' with
> a clear (or otherwise plain) pigment as both beginning and end
> indecies, the 'spiral1 2'texture at index 0.25 and 0.75, for example.
>  Far as the object itself goes perhaps torus slices, rotated and
> translated. Well you did ask  ; )
>
> Bob
>
> Chris Huff <Chr### [at] compuservecom> wrote in message
> news:37D0430E.AA158CC2@compuserve.com...
> > You could approximate a helix with triangles, but I don't think a
> true
> > helix is possible without the isosurface patch.
> > And I think the spiral pattern will do what you want, it isn't
> really a
> > spiral but a kind of helix.
> >

I used half-torus for the springs in my LEGO auto chassis. The problem is,
unless you skew them, you can only use halves and no smaller or the end
surfaces won't be vertical. And with half-torus, you get close to a helix,
but it's up-close noticible that it's not. However, you can skew in POV,
so maybe that's the way to go.

Also, what about other kinds of helixes/spirals? I mean, you gave a method
for a spring-type of shape, but there's many ways to make a helix, for
example like rotating long boxes to get a spiral-staircase effect. What if
it was a ramp, not stairs, though? Anyways, the math (I'm assuming) should
be fairly easy for any helix, maybe they should put it in the next POV
release as a primitive.

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On Fri, 03 Sep 1999 16:27:18 -0500, Larry Fontaine <lfo### [at] isdnet>
wrote:

>Is there any way to get a spiral or helical object without merging (or
>blobbing) a bunch of primitives? And is there a way to get a helical
>texture without an image map? I know there's a spiral pattern, but no
>helical one...

For a helix shape check out the Helix object in shapesq.inc that comes
in all POV distributions.

For a helix pattern, you can approximate it using a density_file. See
the demo scenes that come with POV. If you need additional help with
density_files, don't hesitate to ask.


Peter Popov
ICQ: 15002700

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On Sat, 04 Sep 1999 04:42:13 +0200, Peter Popov <pet### [at] usanet> wrote:

>On Fri, 03 Sep 1999 16:27:18 -0500, Larry Fontaine <lfo### [at] isdnet>
>wrote:
>
>>Is there any way to get a spiral or helical object without merging (or
>>blobbing) a bunch of primitives? And is there a way to get a helical
>>texture without an image map? I know there's a spiral pattern, but no
>>helical one...
>
>For a helix shape check out the Helix object in shapesq.inc that comes
>in all POV distributions.
>
>For a helix pattern, you can approximate it using a density_file. See
>the demo scenes that come with POV. If you need additional help with
>density_files, don't hesitate to ask.
>
You could also use Striscia  http://members.xoom.com/dvarrazzo/epov.htm

Look in povray.text.scene-files for "Kandy for Ken" on 28 June 99.  This is an example
of
wrapping a spiral pattern around a curve using Varrazzo's "Striscia" macro. The image
is
KandyCane.jpg in povray.binaries.images on the same date.
David

------------
dav### [at] cwcomnet
http://www.hamiltonite.mcmail.com
------------

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On Fri, 03 Sep 1999 17:55:54 -0500, Larry Fontaine wrote:
>I used half-torus for the springs in my LEGO auto chassis. The problem is,
>unless you skew them, you can only use halves and no smaller or the end
>surfaces won't be vertical. And with half-torus, you get close to a helix,
>but it's up-close noticible that it's not. However, you can skew in POV,
>so maybe that's the way to go.


Why do the ends have to be vertical, exactly?

Try my spring include file or my torspline include file at 
http://www2.fwi.com/~parkerr/traces.html for a couple examples of 
interesting things you can do with lots of toruses.  The spring 
include file is old (POV 3.0) so you'll need to make a few small
syntax changes, but it uses four toruses per revolution.  If you feed
the torspline file a series of points in a helical shape, it will
obligingly generate the corresponding helix.  It can even do a 
conical spring if that's what you need.  You *might* have to 
calculate an appropriate starting direction to smooth out the
"wrinkles" though.

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Ron Parker wrote:

> Why do the ends have to be vertical, exactly?
>
> Try my spring include file or my torspline include file at
> http://www2.fwi.com/~parkerr/traces.html for a couple examples of
> interesting things you can do with lots of toruses.  The spring
> include file is old (POV 3.0) so you'll need to make a few small
> syntax changes, but it uses four toruses per revolution.  If you feed
> the torspline file a series of points in a helical shape, it will
> obligingly generate the corresponding helix.  It can even do a
> conical spring if that's what you need.  You *might* have to
> calculate an appropriate starting direction to smooth out the
> "wrinkles" though.

I meant shear, not skew.
Vetical assuming your spring goes along the Y axis.
If you have a 90 degree section of a torus, and you scale and rotate it to be
part of a helix, if one end were along the x-y plane the other would not be
along the y-z plane. Which is what you would need for two to evenly meet up.
(And simply reversing the ends on the second one would give the same result as
a half-torus.) However, with shearing, I can take any degree section I want and
shear it along Y to keep both ends vertical.

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Ron Parker wrote:

> Try my spring include file or my torspline include file at
> http://www2.fwi.com/~parkerr/traces.html for a couple examples of

I recently made a variation of this (using macros, i.e. needing
POV 3.1) which solves some equations numerically, so it can't
break apart even for steep helices.

I'll try to post it on povray.binaries.utilities.

Ralf

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On Tue, 07 Sep 1999 16:19:56 -0500, Larry Fontaine <lfo### [at] isdnet>
wrote:

>Ron Parker wrote:
>I meant shear, not skew.
>Vetical assuming your spring goes along the Y axis.
>If you have a 90 degree section of a torus, and you scale and rotate it to be
>part of a helix, if one end were along the x-y plane the other would not be
>along the y-z plane. 
>Which is what you would need for two to evenly meet up.

Not true.  For proof, check the include file on my web site.  (hint:
drop the requirement that one end be coplanar with the x-y plane)

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