Tangent to 2 parabolas in grasshopper

Hi all,
the problem can't be easier to explain and harder to realize: I need to draw a tangent line between 2 parabolas, in rhinocheros we have the command which draw a tangent between two curves, in grasshopper we have not, but in this case it should be easier to program, because parabolas have only 2 possible solution (in this case i think there is only one)...

How can i program it? I thinked about it all day but i can't figure it out. maybe do exist a graphical construction that i ignore?

maybe this can help http://www.math.washington.edu/~aloveles/Math124Fall2012/Conroytang...

Replies to This Discussion

Permalink Reply by David Rutten on November 10, 2015 at 11:52am

I think in these two cases there are no solutions.

Permalink Reply by riccardo foschi on November 10, 2015 at 12:15pm

yea, any idea?

Permalink Reply by riccardo foschi on November 10, 2015 at 12:19pm

I'm trying to figure out how it works, the best idea I got is to draw a tangent to one curve and to slide the point on the curve animating the parameter number and stop the animation when the tangent hit che other parabole, is it possible to achieve?

Permalink Reply by David Rutten on November 10, 2015 at 12:30pm

RhinoCommon does have a method for finding the tangent nearest to two curve parameters, it cannot be used to find all tangents.

Attachments:

tangents.gh, 7 KB

Permalink Reply by riccardo foschi on November 10, 2015 at 1:50pm

how does script node work? do you have a reference site or post with tha basics of it?

Permalink Reply by David Rutten on November 10, 2015 at 1:57pm

Sorry, nothing like that. You need to know C# and then you type your code in there. Knowing your way around RhinoCommon is also a great help.

Permalink Reply by riccardo foschi on November 11, 2015 at 7:32am

The node you programmed is perfect for almost each case, but sometime it don't work, can you explain me how it works, so I can understand when and why it will fail?
is there a way to obtain all the possible tangents as outputs instead of a single one arbitrarily chosen? (i think the maximum number is 2 one could be null or two both)

Permalink Reply by David Rutten on November 11, 2015 at 8:17am

If you upload a case which doesn't work, I can file a report with Seattle HQ.

I ask Rhino for the tangent line closest to the middle of each curve, if the solution is far away from those 'seed' points, it could be that it will not be found. I do not know whether or not this is a legitimate bug. Bear in mind that the tangent finder was written to be used during the Line command, where the user specifically selects the seed points by hand. As such this algorithm is difficult to use from code. Many of Rhino's algorithms suffer from this approach, Curve Offset being another.

I am hopeful that once Rhino6 is ready for shipping the Seattle office will be able to focus on providing more rigorous geometric algorithms to Rhino.

Permalink Reply by riccardo foschi on November 11, 2015 at 9:24am

ok! thanks for the really clear the explanation, so if I understood well you are saying me that there is no chance to obtain all the possible tangents from that script, even if we modify some lines?
That way we could bypass the problem of mid point proximity

Permalink Reply by riccardo foschi on November 10, 2015 at 2:16pm

Yeah I meant if you had some sources where i could learn C#, but you already answered m. :) thank you

Permalink Reply by riccardo foschi on November 10, 2015 at 4:11pm

Why is there only vb and c# nodes in grasshopper? I thougth grasshopper and rhino were programmed with python. If I'd like to start to study a programming language which do you suggest me? I'd like to learn python because i read that it's easier for new users, but if there is no way to use python as a node like you did with c# i think I should go with c#

Permalink Reply by Joseph Oster on November 10, 2015 at 4:25pm