# Nurbs to polyline

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I hope someone know the solution to my problem.

I use extracted nurbs curves as basis for creating cutting paths for CNC-cutters. The path must be 2D so I convert the nurbs to polygons. This is ok for flat surfaces, but for arcs and circles the polygon consists of hundreds or thousands of lines.

I would like to convert the nurbs curve to a polyline, witch would keep arc and circles intact. But there is no convert-to-polyline command.

I hope someone know the solution to my problem.

I use extracted nurbs curves as basis for creating cutting paths for CNC-cutters. The path must be 2D so I convert the nurbs to polygons. This is ok for flat surfaces, but for arcs and circles the polygon consists of hundreds or thousands of lines.

I would like to convert the nurbs curve to a polyline, witch would keep arc and circles intact. But there is no convert-to-polyline command.

2011 can convert NURBS into polylines.

2009 probably not.. At least I didn't find how it could be done ..

I do not see a command in 2011 to convert to a polyline. How is this done?

I do not see a command in 2011 to convert to a polyline. How is this done?

Sorry, you can extract planar - polyline based shapes from solid/NURBS geometry.

I do not see a command in 2011 to convert to a polyline. How is this done?

Sorry, you can extract planar - polyline based shapes from solid/NURBS geometry.

Not really... If the weight of any of the vertices are different than 1, the extract planar option will output a nurbs curve, not a polyline.

What I wish for is weighted polylines, so that we can convert seamlessly between 2D and 3D without loosing information. It seems kinda strange, that it is possible to create planar geometry in 3D nurbs, that cannot be recreated with any 2D tool.

A good example of this is a cross-section of the humble egg. Easy to do with nurbs curves but quite impossible with polylines.

On 12/21/2010 at 1:01 PM, Kaare Baekgaard said:

If the weight of any of the vertices are different than 1

What is the "weight of the vertex?"

I'm not super familiar with the differences between the various types of geometry that are used in Vectorworks. I understand some basic concepts about solids, 3d nurbs, and 3d polygons, but not enough to know what makes them compatable for some operations and not for others, and what exactly is gained and lost by using one or another. Ditto the 2d geometry types.

For example, I have an archway that was created by extruding a 2d polyline that I drew with bezier curves. I then extracted the face of the generic solid archway to create another part with the same curve (a piece of trim that I want to extrude along the path). I understand that if I have saved the history of the extrude, I can copy and paste the polyline back out of the original Extrude object, but I converted to generic solid at some point, that's not an option. It seems that when I use the Extract Face tool, I get a NURBS Surface object, which I can't manipulate with many of the basic 2d drawing tools, and can't get back into a polyline without getting a garbled approximation of the original.

Does any one know of a workaround for this specific problem?

Also, I would greatly appreciate it if someone could point me to some academic texts that go into detail about the nature of 3D CAD geometry. I really value that VW can handle so many different types of geometry, but I'm finding it frustrating to figure out the best workflows when I can't predict why conversion operations break down the way they do.

@mgebel...here's a bit about NURBS in Vectorworks I wrote a little while ago...

Wes

18_VW00279_Workflow_Doc_NURBS_101_horizontal.pdf

@mgebel...something like this???  Operation was done right-to-left...

15 hours ago, mgebel said:

It seems that when I use the Extract Face tool, I get a NURBS Surface object, which I can't manipulate with many of the basic 2d drawing tools, and can't get back into a polyline without getting a garbled approximation of the original.

Does any one know of a workaround for this specific problem?

In this particular case, you may want to try checking the "Create Planar Objects" option under the Extract Tool settings, then extract the surface again. It should hopefully give you the 2D polyline you're expecting.

8 hours ago, Wes Gardner said:

something like this??

Forgive me for being dense, but I am assuming that there is a big difference between a Polygon and a Polyline, as VW defines them? I wasn't able to open your file, as I'm still on v.2019, but I followed the steps and got this result. I am assuming that from this point, there is no way to get back to the Polyline object type?

4 hours ago, Andy Broomell said:

In this particular case, you may want to try checking the "Create Planar Objects" option under the Extract Tool settings, then extract the surface again. It should hopefully give you the 2D polyline you're expecting.

I tried your suggestion, and I did get a polyline back with all of the original reshape edit abilities. Thanks!

4 hours ago, mgebel said:

I am assuming that there is a big difference between a Polygon and a Polyline, as VW defines them?

The only difference is that a polygon (by definition) can have only straight edges, while a polyline could also have curved edges.

But otherwise in day-to-day practice they're rather interchangeable.

13 hours ago, mgebel said:

Forgive me for being dense, but I am assuming that there is a big difference between a Polygon and a Polyline, as VW defines them?

I tend to work mostly with polylines. From your examples above you can see the advantage. In the polygon, the curve is inherently made up of many small straight segments. In the polyline, VW dynamically creates segments for display using the render settings quality level and creates segments for geometry (eg. when you make an extrude) using the 2d Conversion Resolution preference. The polyline curve is defined mathematically as a curve or series of curve segments.

Kevin

8 minutes ago, Kevin McAllister said:

I tend to work mostly with polylines. From your examples above you can see the advantage. In the polygon, the curve is inherently made up of many small straight segments. In the polyline, VW dynamically creates segments for display using the render settings quality level and creates segments for geometry (eg. when you make an extrude) using the 2d Conversion Resolution preference. The polyline curve is defined mathematically as a curve or series of curve segments.

Kevin

Polylines are indeed better... just be careful that a polyline can also contain Bézier and cubic... which not all CNC can handle.

Obviously Kevin's and Andy's method is more efficient as you end up with a polyline (with WAY few control points) 🙂

Posted (edited)

Found this post and noticed when I follow the steps, if I'm not in top/plan view I end up with a polygon that matches the screen view. If I do it in top/plan and then switch the plane to Layer plane it works like a charm.

Edit: Found that create Planar Objects in the extract tool prefs yielded the results I was looking for. 🤦‍♂️Read the whole thread next time

Edited by trashcan

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