Can i draw an arc with a specifying circumference value

[simon le bon]

I have needed several times to draw an arc with a specifying circumference Value.
SketchUp give us the rope and the radius, and we just know how long the arc is into the info dialog box.



I have searched hard to find out, but it seems not existing simple mathematic relation between the couple radius/rope and the desired circumference value.. So,,, i'm certainly not the first with this question.

simon.

[Jean Lemire]

Hi Simon, hi folks.

There are an infinity of arcs that can be drawn if only the length along the circumference is know.

You also need either the radius or the angle.

You can use the formula : ARC = R * A

Where ARC is the arc length, R is the radius and A is the angle

See attached SU file for ideas.

---

Arc using angle and radius.skp

[pilou]

And A is in Radian
(but that was in the tut above

[Gaieus]

There is also a ruby script by Didier for drawing arcs in different way and which you may find useful.

[remus]

I dont know of any way to do that thats native to SU, but there might be a ruby out there that does this. Im pretty sure itd be possible with ruby if such a script doesnt already exist.

edit: sorry i thought you said radius youd be much better of listening to jean.

[pilou]

Go there: choose your unities and enter only your length Rope A B, your length of the Arc circle whished and Press "Calculate"
---> you will obtain the Radius! And the Apothem & Height of Arc necessary
So now you can draw your arc of circle between A and B in SU
PS Of course that is meaning that you have Internet On
THat is a very cool site: many other Calculators inside!

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[simon le bon]

Thanks so much Pilou

Exactly what i needed. And i guess i will not be the only one to keep this link in my link's tool box.

simonlebon

[pilou]

Of course precision depend of the number of decimals

Maybe Didier Bur can makes something? A little ruby script?

Mais sinon cela le fait bien!

[simon le bon]

Dear Remus,Pilou,Gaieus and Jean,

I'm afraid i haven't found into your replies exactly what i'm searching for.

What i need sometimes would be drawing an arc from point A to B and tape the length around the arc in the VCB (in place of the rope), leaving SU decide corresponding radius.
//
I Know A and B so i know length rope (rope)
I know length around the arc (arc it's the value i want.

I don't know angle (A), neither Radius (R)
//
(mathematic is a strange land to me)
If i want an arc=t , i have to found R and A with rope value.

R= arc/A
and
R= rope/2sin(A/2)

=> arc/rope= A /2sin(A/2) >> for me it's the end of the travel

//
others relations:

A = 2 x arcsin(rope/2R)

and ???§§§!!!=**@@

Sorry for so trouble