Biarc Component Question

Hello everybody!

Im currently working with biarcs, and so using the biarc component. Im afraid I don't fully understand its inputs.

When it comes to the tangent vectors and the ratio, what exactly is it asking for?

Some people plug a multidimensional slider into the vectors inputs and a slider into the ratio, but I am not sure of what they control.

Thanks in advance for any insight.

Replies to This Discussion

Permalink Reply by David Rutten on October 8, 2016 at 2:06pm

A single circular arc is fully defined by two end-points and a start tangent. There's only one possible arc that fits those three criteria. However sometimes you want to specify the tangent at both ends and still end up with arc-like geometry.

A bi-arc curve solves this problem by creating a pair of arcs. The first arc starts at the first point and its start direction is parallel to the first tangent. The second arc ends at the second point and its end direction is parallel to the second tangent. Somewhere in between the two arcs meet in a tangent-continuous fashion.

So the start and end-point inputs specify where the bi-arc starts and ends, and the tangent inputs specify the bi-arc direction at the start and end point.

In actual fact there is an infinite number of different arc pairs that satisfy the above constraints (just like there's an infinite amount of circles through two points). The Ratio input helps you to select one particular instance from this infinite set. Unfortunately the ratio is not easily explained, but basically it allows you to balance the length of the first arc vs. the length of the second one.

I suppose you could use a 2D slider to specify tangents, wouldn't be my first choice though.

Permalink Reply by ShynnSup on October 10, 2016 at 1:19pm

Hmmm thanks David. I asked because I was studying how to vary a bench with the bi arc component, and what happened is that with slight changes in the ratio the curve changed drastically, and so when I changed the 2D slider coordinates.

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