topic Re: Using GDL to write parameterized iron chains in GDL

Using GDL to write parameterized iron chains

yongler — Sun, 26 Mar 2023 07:06:58 GMT

In some scenic spots in Hangzhou, China, chains are used as railings, and the top of pagodas is fixed with iron chains. Like the picture. This kind of iron chain is written in GDL language. The hot spot at one end can be dragged, and the sag arc in the middle can also be controlled. Another key parameter is that each iron ring rotates by 90 °

Re: Using GDL to write parameterized iron chains

Hmooslechner — Sat, 25 Mar 2023 16:46:13 GMT

Interesting - i tried to code somethng like that, but unfortunately, i was not able to do the maths on that. How can we get this?

Re: Using GDL to write parameterized iron chains

Barry Kelly — Sun, 26 Mar 2023 05:04:01 GMT

The math for the curve should be pretty straight forward.

I believe it is called a catenary curve.

The link in the chain is another matter, and one I probably wouldn't attempt.

The link itself would be quite easy and the rotating 90° for each alternate link is also quite easy.

In a straight line it would be no problem.

But for each link in the curve, you will have to calculate the position in the curve and how much it deviates along the length axis for that particular link.

That will be the tricky part, and I am sure it can be done mathematically, but it is a bit beyond me (a bit of Googling or chatGPT maybe?)

The coding may or may not end up quite concise and not too large, but the polygon count of the final object cold be a great hindrance to your model.

I would consider modelling as a TUBE (either square profile or thin rectangle rather than round) and applying a chain surface material (might not map correctly on a round profile).

Barry.

Re: Using GDL to write parameterized iron chains

Hmooslechner — Mon, 27 Mar 2023 05:03:25 GMT

i did somethings like this: https://bimcomponents.com/GSM/Details/25256

You discribed my "mathematical problems" on that very well. You have the curve, but You must get the same distances for the Chain-link-parts ON THIS CURVE. I could not solve that by myself.

Re: Using GDL to write parameterized iron chains

yongler — Sun, 26 Mar 2023 05:47:55 GMT

The current version is an arc curve, not a gravity parabola😥. The calculation of the distribution of each link on the circular arc curve is relatively easy.

I will send the gsm file later.

Re: Using GDL to write parameterized iron chains

yongler — Sun, 26 Mar 2023 06:09:37 GMT

The gsm file is here：

Re: Using GDL to write parameterized iron chains

yongler — Sun, 26 Mar 2023 06:13:05 GMT

Wow.Great ! This is the real gravity curve

Re: Using GDL to write parameterized iron chains

Hmooslechner — Sun, 26 Mar 2023 07:04:52 GMT

Its a very simple solution and nobody will see the difference to "a real catenary curve" as long, as its sufficiantly tightened. Well done. Very well done!

Re: Using GDL to write parameterized iron chains

yongler — Tue, 28 Mar 2023 00:50:01 GMT

It seems that ChatGPT doesn't understand GDL yet, so GDLer hasn't been replaced so quickly 🤔

Re: Using GDL to write parameterized iron chains

Barry Kelly — Tue, 28 Mar 2023 00:59:58 GMT

ChatGPT can only learn from resources it can find on the web, and we struggle with that when it comes to understanding GDL. 😂

It can't help you with the GDL side of things, but it might be able to give you a formulae to calculate the angle of each link in the curve.

Barry.

Re: Using GDL to write parameterized iron chains

Laszlo Nagy — Tue, 28 Mar 2023 17:44:06 GMT

Yeah, ChatGPT is a GDL Noob. 🙂

Re: Using GDL to write parameterized iron chains

yongler — Wed, 29 Mar 2023 03:25:34 GMT

GDL is not popular, so developers of chatGPT have not input GDL information?

GDL may be the forever blind zone of chatGPT ? 😎

Re: Using GDL to write parameterized iron chains

Hmooslechner — Sat, 01 Apr 2023 10:45:59 GMT

Maybe a rope instead?

Make Your own... with the profilemaker and my GDL - a few changes in 3D-script:

Re: Using GDL to write parameterized iron chains

yongler — Sun, 02 Apr 2023 12:32:00 GMT

Re: Using GDL to write parameterized iron chains

julienK — Sat, 08 Apr 2023 11:50:03 GMT

I managed to achieve this with a proper catenary curve.

As Hmooslechner mentioned the hard part was to get equidistant points along the curve to generate the chain links. I used an approximation method that works just fine.

I converted this method found on YouTube https://www.youtube.com/watch?v=gkdnS6rISV0 to work in GDL, but this method generates points at fix intervals along the X axis so the greater the slope the greater the distance between points along the curve.

To fix this I calculate the tangent angle at point n on the curve then generate the point n+1 at cos(tangent angle) along the x axis. This generates equidistant points along then curve.

Both anchors can be moved around

The length of the chain can be adjusted without moving the anchors.

The links of the chain are fully customizable.

And it can be displayed as a cable

Re: Using GDL to write parameterized iron chains

Hmooslechner — Sat, 08 Apr 2023 12:03:35 GMT

That was much too much maths for me! 😂 - Where and when and how will we (the cummunity) get this? 😇

Re: Using GDL to write parameterized iron chains

julienK — Sat, 08 Apr 2023 13:00:00 GMT

I'll make a commercial version available for purchase on monday. PM me if interested.

Re: Using GDL to write parameterized iron chains

jl_lt — Sat, 08 Apr 2023 13:57:23 GMT

For those of us who ever toyed with the idea of trying to learn gdl, this has been beautiful to read and terrifying at the same time. I congratulate you all guys

Cheers!

Re: Using GDL to write parameterized iron chains

Hmooslechner — Sat, 08 Apr 2023 14:45:31 GMT

In my mind, some solutions for that without the intensive amounts of maths are rumbling in the cellars of my mind, but i can wait to realize them until You have made Your money.. How long do you think I should wait until your expenses are financially recouped? 😇