Offset multiple curves inwards

Replies to This Discussion

Permalink Reply by Hyungsoo Kim on November 9, 2017 at 9:45am

Hi.

Looks like your curves are not consistent in directions. Try "Clipper" plug-in.

The "Polyline offset" component from clipper plug-in allows you to select the polyline as the inner offset result("H" output)measuring the length of shorter one by offsetting a polyline on both sides regardless of direction.

Permalink Reply by peter fotiadis on November 9, 2017 at 11:01am

Indeed.

BTW: the classic way to check orientations is to test the DotProduct between the Z derived from a polyline Plane and some suitable "standard" vector (it could be the Z of the first plane in the polyline List, for instance). If is negative you reverse the polyline. There's another Method in RhinoCommon as well for that but requires code (and planar curves).

Permalink Reply by Petras Vestartas on November 9, 2017 at 12:34pm

How it looks in code? :) For checking directionality of polyline winding?

Permalink Reply by peter fotiadis on November 9, 2017 at 1:00pm

I'll post some C# example soon.

BTW: Given the opportunity I have no idea what Clipper does ... but does that? (yellow is GH/Rhino offset, the other is the correct thing (+ same "orientations"))

Permalink Reply by Andrew Heumann on November 9, 2017 at 1:30pm

this is way more complicated than it needs to be in GH. Just take all your closed curves and flip them with a circle (that only has to be roughly parallel to your curves) as the guide curve. Voila, all your curves are now winding consistently (and will therefore offset consistently)

Permalink Reply by Laurent DELRIEU on November 9, 2017 at 12:55pm

Most of the time I do that, but as Rhino Offset is bad I tend to use clipper.

I just do the 2 offset positive negative and measure the length of the curve and I take the min length. 

Permalink Reply by Alex Duro on November 9, 2017 at 2:14pm

Quite efficient and easy to do the double-offset with selection of shorter curve...

Thank you!!