what's gravity got to do with it.?

I have a catenary...points a and b are set by defining a circle on a world xy plane point, and intersecting it with a line from rhino.

but the points a and b do not define the start and end points of the catenary... why is that?

In the attached example and picture you can see that I have a 3 slider input vector generator...

Whenever the x is at 0.0 the start and end points of the catenary swap places...

Any explanations / remedies welcome...

I have another much more complex definition where this is awkward to handle.

Attachments:

gravityquestion.3dm, 27 KB
gravityquestion.gh, 5 KB

Replies to This Discussion

Permalink Reply by Chris Tietjen on March 22, 2013 at 9:47pm

Consider the catenary under the influence of gravity (concave up). If the vertex is at (0,0) then because a catenary is always similar to itself just use two equations and approach the vertex from each side separately. Rotate as required.

Attachments:

gravityquestion2.gh, 23 KB

Permalink Reply by roderick read on March 23, 2013 at 11:25am

Thanks for the reply Chris,

That's a neat way to generate a very good catenary...

The catenary component in .gh may well be generating like this and the vertex is assumed to have a frame of refrence generated from the input points, their centre, and vector from that centre-to-0,0 with a (amplitude dependant on the spare length over points distance and direction of vector )...

Your model vector display stays -ve Z when a is either -ve or +ve

but changes in x... It's like the .gh catenary component I think.

hmmm. Can anyone give advice on how to start sandboxing experimental versions of my own catenary component?

It's important for me to have the A and B set points fixed as I am lofting this and other offset catenarys... if the catenarys or "gravity" vector move then it throws the whole model lofting.

Permalink Reply by Chris Tietjen on March 23, 2013 at 3:19pm

Can you draw a portion of what you're trying to accomplish overall in terms of the lofting as I'm not sure that I understand where the problem is. It seems like you should have what you need at hand already so I must be missing something.

Chris

Permalink Reply by roderick read on March 24, 2013 at 1:57pm

Thank Chris, ok I'll post the current whole .gh tonight... ummm it's massive .

So what I'll do is also make a wee video of what's going on in it, post it to youtube ... come back here with the link and ... repost a chopped down version of the .gh again afterward... might not be finished until tomorrow though... busy busy

Attachments: