How do I control the curvature of an arc

Hi, I have 3 points, A, B, and C, I want to make 2 arcs, one from points A and B, and the other one from points B and C. I have the arcs, but is there a way to control the curvature of the 2 arcs so that they look similar to the ones in the pictures I attached.

Thanks

Yan

Attachments:

3cc.JPG, 100 KB
3a.jpg, 479 KB

Replies to This Discussion

Permalink Reply by Suryansh Chandra on July 12, 2010 at 12:35pm

Curve>Spline>BiArc

Permalink Reply by David Rutten on July 12, 2010 at 12:47pm

Two points do not define an arc. Or rather, you can fit an infinite number of arcs through any two points. What you need is either a third point, or a radius value, or a start tangent vector.

Your [BC] arc is easy, you just copy the end-tangent from the [AB] arc in order to make the two tangent at point B. How you then choose to define [AB] is up to you.

Suryansh' suggestion might be of interest to you as it is a great way to create tangent arcs. It doesn't however allow you to specify the B point, so it may not be a useful component for this particular project.

--
David Rutten
david@mcneel.com
Poprad, Slovakia

Permalink Reply by Yan Huang on July 12, 2010 at 5:55pm

I am very new with GH, this might be a simple question, but how to I come up with a tangent?

Permalink Reply by Leon Deng on July 12, 2010 at 7:37pm

I had the same problem when I was doing the same homework. I just discovered a component called Evaluate Curve (Curve>Anaiysis>Evaluate Curve), you need to provide the curve, the point where you take the tanget. Then connect the tangent vector to the "D" input grip of the Arch SED. That way the second curve will be come dependent of the first curve.

Permalink Reply by Yan Huang on July 12, 2010 at 7:50pm

What do you mean by i need to provide the curve? I need to draw it on rhino instead of using GH?

Permalink Reply by Leon Deng on July 12, 2010 at 8:35pm

By that I mean that you need to define a curve first. For my homework, I define the first curve by using the 3pt arc component. With the 3pt arc, you need to connect Point A (first point) and point B (end point), you also need a intermediate point (define by using slider). once you have three points, you can define a curve and this is the curve you need to hook up to the Eval Curve component. Hope this help.

Permalink Reply by Yan Huang on July 12, 2010 at 9:29pm

I tried this, but the "evaluate curve" component point doesn't match point B, where the tangents of the two arcs [AB] and [BC] should be the same.

Permalink Reply by Jon Mirtschin on July 13, 2010 at 1:18am

Hi Yan,

I did set up yesterday the basis of how I would setout (in 2d) the arcs for your 3 point truss, will today give it 3d arrangement and add structural profiles. I found problems with plugging arcs into evaluate curve component, always seems to output properties at the start of the arc (David might verify if this is a bug).

See if the attached is consistent with how you would like to achieve this.
The arcs are controlled by the points in the Rhino model.
Cheers,

Jon

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