Grasshopper

algorithmic modeling for Rhino

# Conform Curves

Hi,  I have been trying to create a simple interaction in Kangaroo where a circle would collapse around a series of arbitrary lines or closed curves.  I can't seem to make this work using the UnaryForce object.  Would it be better to assign Springs only?

Glenn

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See the attached definition for one approach to this.

It uses a combination of springs and an attraction force to pull the curve inwards, and springs with cutoffs for the hard circles.

Attachments:

Thanks Daniel, much appreciated.

I noticed that the conformed geometry very closely approximates the inner circles, but does not overlap.  What causes this minor variation?

Glenn

Hi Daniel,

I can see very clearly from your example how the cutoffs work after playing around with it for a while.  This is great!  Is there a way to use the inner geometry to drive the conforming process so that the inner curves can vary?  I have tried extracting the points and lines from the inner circles to feed into the anchors but I get unexpected results.

Glenn

Hi Glenn

You have to support different rest length and cut off values and duplicate them according to count of the segments.

Cheers,

[uto]

Thanks [uto],

I will try that.

Glenn

At the moment to use curves for collisions you have to divide them into points and use a series of balls (springs with cutoffs) at these points. By insetting the curves before division you can make this collection of balls correspond reasonably closely with your shape.

Bear in mind that results obtained this way will always be approximate because we are discretizing the curves into a number of points, and using very fine subdivisions with thousands of points will get quite slow.

Here I have used equal sized balls, which will work ok for fairly rounded shapes.

For more angular shapes you could centre the balls on the medial axis of the curve and vary the radii.

Attachments:

Hi Daniel,

Thanks for the detailed explanation, this is very helpful.  The medial axis reference has also given me more ideas, perhaps useful if I want the outer curve to conform more to the concavities of the inner shapes.  I will try that as well.

Glenn

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