Adjusting the chord length of an arc while keeping arc length the same

seth.noble · ‎01-05-2023

I am currently trying to create an adjustable arc that has a locked arc length with an adjustable chord length. I found some examples on here and YouTube for doing this based off of radius, but I just can't seem to figure out how to do it with chord length.

YouTube tutorial : https://www.youtube.com/watch?v=7deBFOuH0lM&t=414s

-This was very useful knowledge, but I could not get the formulas to work when trying to make a cord length formula. I would always end up making a circular chain of references.

Revit Forums: https://forums.autodesk.com/t5/revit-architecture-forum/control-radius-on-adaptative-family/td-p/103...

-Same issues as the YouTube tutorial but it was still useful knowledge

This is my current example that is based off of radius

How it is being used in a project

I change the radius to 1' and then line it up to the column

Although using the radius works for now, my end goal is to make this but you are adjusting the chord length of an arc instead. I have found ways to do this, but none of them are able to keep the arc length the same and automatically adjust the radius for you.

If you need information please let me know!

ToanDN · ‎01-05-2023

Have you looked at this?

https://www.revitforum.org/node/1126

seth.noble · ‎01-05-2023

Yes I did. I actually recreated it so I could mess around with the formulas to get them working for me.

Unfortunately I still run into the same issue. I am wanting the arc length locked to a certain length and have the radius of the arc auto adjust when I change the chord length. For this example I would only be adjusting Width. R would auto adjust while s stays the same

ToanDN · ‎01-05-2023

Post your family here.

barthbradley · ‎01-05-2023

I don't understand the gymnastics here.

You want to adjust the chord length of an arc while keeping arc length the same? So basically, you want to parametrically change the central angle and/or radius as well as the length so that the length remains consistent (e.g. the same length no matter what the central angle and/or radius is). Is that about the size of it? If so, WHY? Serious question. Looks to me like you are applying cladding to a round column. That's a piece of cake that doesn't require an advanced degree in Mathematics to model.

seth.noble · ‎01-05-2023

Yes you are correct. Form the picture your provided, I want to be able to change the distance from O to P while L is locked. Say L=3", no matter what distance from O to P is (unless the number is larger than 3" in which case it would error out), L would still be 3". To answer your question on why, that is how my work wants it (if possible). The example given in the post is was only for a basic visual representation and does not fully apply to what we are trying to do. I would provide a better example but this was the only one I had available at this time. I don't know if it is even possible and with my basic knowledge I could not find any way to make it work.

ToanDN · ‎01-05-2023

You have enough to information (fixed arc length, radius) to make the formula work (arc angle) so I am not sure what you are still wondering. File attached.

barthbradley · ‎01-05-2023

@seth.noble wrote:
To answer your question on why, that is how my work wants it (if possible).

Yes, but WHY does your work want it done that way? Maybe they are wrong-thinking. Just saying. 😉

seth.noble · ‎01-05-2023

@ToanDN wrote:
You have enough to information (fixed arc length, radius) to make the formula work (arc angle) so I am not sure what you are still wondering.

It has been a few weeks since I last worked on this project so sorry in advance if I mess up any terms/formulas! I was getting arc length from the formula: Arc_Length * 180° / (pi() * Radius). When I then tried to add another formula to keep arc length the same when adjusting chord length, it would end up making a circular chain of references and not allow me to proceed further. I tried a few other formulas, but I kept failing at getting it to work. I would post those formulas but I think I ended up deleting that example 🙁

ToanDN · ‎01-05-2023

@seth.noble wrote:

🙁

Did you open the file I posted?

seth.noble · ‎01-05-2023

@barthbradley wrote:
@seth.noble wrote:
To answer your question on why, that is how my work wants it (if possible).

Yes, but WHY does your work want it done that way? Maybe they are wrong-thinking. Just saying. 😉

I wish I could explain more and honestly you could be right 😅, but if it is possible I then could present both versions (one based off of radius and the other based off of chord length) and show the advantages and disadvantages between the 2.

seth.noble · ‎01-05-2023

@ToanDN wrote:
@seth.noble wrote:
🙁
Did you open the file I posted?

I somehow scrolled past it 😅. I think this is the correct solution! I will double check and mark the post as solved if it is. thank you so much!

seth.noble · ‎01-05-2023

@seth.noble wrote:
@ToanDN wrote:
@seth.noble wrote:
🙁
Did you open the file I posted?
I somehow scrolled past it 😅. I think this is the correct solution! I will double check and mark the post as solved if it is. thank you so much!

Sorry I might have jumped the gun on that one. So this seems to be almost the same as the original I posted. I am trying to get a formula that has a fixed arc length and an adjustable chord that will change the radius to fit the arc length. This is using the radius to change the chord length instead if I am correct.

The blue line (chord length) would be adjusting radius(r) so that Arc Length (L) will stay the same.

ToanDN · ‎01-05-2023

@seth.noble wrote:

Sorry I might have jumped the gun on that one. So this seems to be almost the same as the original I posted. I am trying to get a formula that has a fixed arc length and an adjustable chord that will change the radius to fit the arc length. This is using the radius to change the chord length instead if I am correct.

The blue line (chord length) would be adjusting radius(r) so that Arc Length (L) will stay the same.

Using the chord length to constrain doesn't make any practical sense. If you are trying to provide a column wrap then you already have:

- the column radius given

- the arc length given

So the only thing you need to do is plug those two in to get the two red points showing up there. Knowing the length of the chord has absolutely no value in this equation.

seth.noble · ‎01-06-2023

@ToanDN wrote:
@seth.noble wrote:
Sorry I might have jumped the gun on that one. So this seems to be almost the same as the original I posted. I am trying to get a formula that has a fixed arc length and an adjustable chord that will change the radius to fit the arc length. This is using the radius to change the chord length instead if I am correct.

The blue line (chord length) would be adjusting radius(r) so that Arc Length (L) will stay the same.

Using the chord length to constrain doesn't make any practical sense. If you are trying to provide a column wrap then you already have:
- the column radius given
- the arc length given
So the only thing you need to do is plug those two in to get the two red points showing up there. Knowing the length of the chord has absolutely no value in this equation.

The column was only used as an example to give a basic idea of what I needed and show what I had so far. The equation I am looking for needs to have chord length as the input parameter and for radius to automatically update so arc length would stay at a fixed length. If that equation is possible.

ToanDN · ‎01-06-2023

So if the column wrap example is a wrong application then what is a correct one?

seth.noble · ‎01-06-2023

@ToanDN wrote:
So if the column wrap example is a wrong application then what is a correct one?

Using radius as the input is not exactly wrong. I am trying to make an example of using the radius and another example using chord length. The column was just the best way to test things on. I have the radius on already figured out, but I don't have an formula using chord length. The radius based off of a chord length input (and arc length locked) was asked of me to create if it is possible.