Grasshopper

algorithmic modeling for Rhino

Lines normal to curves directonal issues

After 3 days of trials and errors I decided to throw my towel and ask for help.

My problem is (I think) simple to understand and, as far as I have read from the posts, quite common as it is related to the way GH defines a plane on a planar curve.

Here it is:

I have a number of curves extracted by intersecting a surface with a plane. 

I would like to draw lines at equal intervals normal to these curves.

The problem is that since these curves are a combination of convex and concave the direction of the curves normal to it is difficult to control. as you can see from the files the planes x & y axis is rotated 180deg.

I believe is a similar issue related to Offset Curves.

Here attached are the base files and relative screenshot.

Thanks in advance to your help.

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Permalink Reply by Pieter Segeren on June 15, 2015 at 4:32am

Hi Nikos, I'm not sure I understand: I think the attached definition does what you described, or?

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Permalink Reply by nikos tzar on June 15, 2015 at 11:48am

In your definition all the planes rotate so that their X axis points towards the direction of the given vector.

I believe what Roberto is after (I am not really sure I got it right, though) is just to rotate 180 degrees the planes that have X pointing towards the "wrong" side.

The difference is more clear in plan view:

Again, I can't be sure this is exactly what Roberto is after. I am merely pointing out that the result is not the same in those 2 approaches.

Cheers, Nikos

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Permalink Reply by nikos tzar on June 15, 2015 at 4:03am

Hello Roberto,

The way I see it, the "right side" of the curve can only be determined by a user input. (we cannot say, for example, it is towards the World X axis).

So all I could come up with is to define a point on the "right side" of the curves and rotate the planes that don't point towards this point:

If you move the point to the other side of the curves, the planes will follow it.

this is not a concrete solution but I hope it will work ok in your case...

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Permalink Reply by Roberto on June 15, 2015 at 7:18pm

Nikos,

you understood perfectly and from a first look at your definition it looks like its working.

Let me spend a some time digesting it and testing it.

In the meantime i give a big THANK YOU. You have no idea how many times I banged my head against the wall on this one.

thanks again..

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