"Chris B" <nom### [at] nomailcom> schreef in bericht 
news:4a1e7ec8@news.povray.org...
>> And presumably you're using either catenaries or a
>> full mechanics simulation to produce hanging curves...?
>
> Ahh! Nothing nearly so sophisticated there I'm afraid :-). I have a loose
> segment macro that takes the current point and a new point and adds an 
> extra
> point in between roughly in the right place to bring the rope length to
> approximately the value specified as a parameter and to get the lowest 
> point
> roughly where it should be for the relative heights of the two end points.
> Then it relies upon using a curved spline for that segment of rope to join
> the dots in a fairly gravity compliant way. There's nothing stopping 
> anyone
> with a better grip on the maths adding such a macro though. Each of the
> path-defining macros is quite short, so it doesn't take long to add new
> shape macros.
>


Yum yum... for the ropes and knots....  :-)
For catenaries, there is a set of macros by PM2Ring (2005) which do a better 
job than the catenaries by Chris Colefax. There is also a set of macros by 
Rob Antonishen (2002) but they do not work quite well I am afraid (last 
timeI tried them, earlier this year). Both sets were made available in these 
forums at the time.

Thomas

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"Thomas de Groot" <tDOTdegroot@interDOTnlANOTHERDOTnet> schreef in bericht 
news:4a1e9c33> For catenaries, there is a set of macros by PM2Ring (2005) 
which do a better
> job than the catenaries by Chris Colefax. There is also a set of macros by 
> Rob Antonishen (2002) but they do not work quite well I am afraid (last 
> timeI tried them, earlier this year). Both sets were made available in 
> these forums at the time.


Found the PM 2Ring Catenary macro in povray.binaries.scene-files and in 
povray.text.scene-files: "Catenary - a chain making macro" 2 September 2005

I am unable to trace Rob Antonishen's macro.

Thomas

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"Chris B" <nom### [at] nomailcom> wrote:
> >> I'm working on a new Rope macro ...

Now *this* looks good...!

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> Thoughts/ideas welcome.
> 

Wow!

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"Bill Pragnell" <bil### [at] hotmailcom> wrote in message 
news:web.4a1e750b99a5bfb66dd25f0b0@news.povray.org...
>
> ... can you handle e.g. coiling automatically?
>

I've added a bit more into the spiral macro. What d'you have in mind by 
coiling 'automatically'?
The example below uses two calls to the macro. The first adds a little helix 
of two coils in the middle, spiralling downwards, the second call adds the 
outward spiral (both using the default amount of randomness).

Regards,
Chris B.

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Attachments:
Download 'rope_17.jpg' (16 KB)

Preview of image 'rope_17.jpg'

"Thomas de Groot" <tDOTdegroot@interDOTnlANOTHERDOTnet> wrote in message 
news:4a1e9c33$1@news.povray.org...
>
> "Chris B" <nom### [at] nomailcom> schreef in bericht 
> news:4a1e7ec8@news.povray.org...
>>> And presumably you're using either catenaries or a
>>> full mechanics simulation to produce hanging curves...?
>>
>> Ahh! Nothing nearly so sophisticated there I'm afraid :-). I have a loose
>> segment macro ....
>
> For catenaries, there is a set of macros by PM2Ring (2005)

What a tough assignment that turned out to be   ;o)

I couldn't quite get my head round the approach that PM2Ring took, so I 
spent the weekend swotting up on the maths (with long breaks for the 
headaches to subside), and worked out a way to just use the most rudimentary 
catenary formula. So it uses the value of 'a' to control the shape, which is 
the ratio between 'H' (the horizontal component of the tension in the rope) 
and 'w' (the weight per unit length).

The method used by PM2Ring has the advantage that you can specify the ratio 
between the straight-line length and the rope length to control the amount 
of sag in the rope, which is probably more intuitive than using 'a'. 
Nevertheless, I plan to finish the documentation and post the first version 
of the code in a couple of days. Then if anyone can improve on it we could 
incorporate that in a future version.

So here's the result. An image of the catenary juxtaposed behind my original 
with 'fake' gravity.

Regards,
Chris B.

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Download 'rope_04.jpg' (25 KB)

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"Chris B" <nom### [at] nomailcom> schreef in bericht 
news:4a256926@news.povray.org...
> What a tough assignment that turned out to be   ;o)

Good work! I am always awed by people able to do these tricky things. I know 
I cannot. Thanks indeed for the effort.

Thomas

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Whoops, sorry for late reply, got caught up with HDRs :)

"Chris B" <nom### [at] nomailcom> wrote:
> "Bill Pragnell" <bil### [at] hotmailcom> wrote in message
> news:web.4a1e750b99a5bfb66dd25f0b0@news.povray.org...
> >
> > ... can you handle e.g. coiling automatically?

> I've added a bit more into the spiral macro. What d'you have in mind by
> coiling 'automatically'?

I meant 'loose' coiling, where the rope can pile up on itself, or a hanging
loose coil (hooked over something, for example). I realise these are
non-trivial, I expect people can model this manually given your tools - just
wondered, that was all! :-)

This is a great macro, keep it up!

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"Chris B" <nom### [at] nomailcom> wrote in message 
news:4a1e679e@news.povray.org...
> I'm working on a new Rope macro to handle knots and track object surfaces

I've posted the first version of these macros onto the POV-Ray Object 
Collection at:
http://lib.povray.org/collection/rope/chrisb%201.0/rope.html

This image shows the predefined styles you can use. It's easy to add your 
own styles and fairly easy to add new types of knot etc.. I'd be happy to 
incorporate any new styles or new knots that you develop into a future 
version.

Chris B.

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Attachments:
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"Bill Pragnell" <bil### [at] hotmailcom> wrote in message 
news:web.4a2631e799a5bfb66dd25f0b0@news.povray.org...
>
>> > ... can you handle e.g. coiling automatically?
>
>> What d'you have in mind by coiling 'automatically'?
>
> I meant 'loose' coiling, where the rope can pile up on itself, or a 
> hanging
> loose coil (hooked over something, for example). I realise these are
> non-trivial, I expect people can model this manually given your tools - 
> just
> wondered, that was all! :-)
>

Here's an example of what the randomisation options can do with a bit of 
fiddling around. Some of the random shapes looked unrealistic, so it was a 
question of repeatedly adjusting the seed until I got reasonable looking 
shapes. This doesn't use any form of collision detection, so eagle-eyed 
observers will notice that some bits of rope pass through other bits of rope 
and even into adjacent objects in places.

The foreground object uses a very high randomisation setting at about 30 
times the default. The other two are copies of the same coil at about 15 
times the default randomisation (the one on the post is rotated and scaled 
down a little).

To really overlay the coils of rope so that you don't get collisions would 
be more complex. I've had a few ideas, but I'm not sure how difficult any of 
them would turn out to be to implement. Most of my ideas to date would risk 
ending up with some very limp-looking rope.

Regards,
Chris B.

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