topic Re: Polylines are too dense to magic wand for mesh contour in Collaboration with other software

Polylines are too dense to magic wand for mesh contour

Robert Nichols — Tue, 22 Apr 2025 15:40:11 GMT

My usual workflow to go from surveyor's work to an ArchiCAD mesh is to use the magic wand on the surveyor's poly line contours to create a contour or ridge on the mesh. The surveyors did a good job of providing a single poly line for each contour - so often the contours are broken by labels, requiring a lot of clean up work.

BUT...the polyenes are super dense: there is a vertex, or node, every 2". At the scale of this site, the average contour has over 14,000 nodes. There are about 70 contours across the site, making for a very slow mesh. Adding additional contours, setting z-values, is really annoying.

Q1: Is there a way to increase the "coarseness" of the wand operation? So the wand only reproduces every third node of the poly line, for example?

Q2: Does ArchiCAD have a tool, that I'm not aware of, that can reduce the resolution of a poly line? My civil engineer asked me if I had tried "de-curving" the polylines, which I suspect is language that comes from Revit, or some other platform. Sounds great, but I don't think I have such a tool in ArchiCAD. Am I wrong?

Any other suggestions?

Re: Polylines are too dense to magic wand for mesh contour

Barry Kelly — Wed, 23 Apr 2025 03:17:28 GMT

Change your Magic Wand settings to 'Linear Segments' rather than 'Best Match'.

Then you can play around with the other settings for deviation from curve or segments along arcs to get the results you want.

Barry.

Re: Polylines are too dense to magic wand for mesh contour

danielk — Wed, 23 Apr 2025 10:57:53 GMT

Hi,

I think the setting Barry mentioned controls how the magic wand traces curves, not straight segments. So, in case you have a curve, it will definitely help, but if you just have a very detailed polyline with straight segments, I think there is no setting in Archicad that would help.

We also use Rhino at my office, so when this happens, I just open the dwg in Rhino, and reduce the number of segments there (or if I already have the polylines in Archicad, I do it in Grasshopper).

If you don't have Rhino, I am not sure what else you could do using only Archicad...

Kind Regards,

Daniel

Re: Polylines are too dense to magic wand for mesh contour

Barry Kelly — Wed, 23 Apr 2025 11:18:44 GMT

@danielk wrote:

I think the setting Barry mentioned controls how the magic wand traces curves, not straight segments.

This is true, I was thinking of a spline for the contour rather than a polyline that you mentioned.

In the case of many straight segments in the polyline, you will need to manually place a contour selecting specific points along the polyline rather than magic wanding.

There is a 'line consolidation' tool that will reduce the number of points, but only if the segment are co-linear.

Barry.

Re: Polylines are too dense to magic wand for mesh contour

Yves — Wed, 23 Apr 2025 12:08:02 GMT

Hi,

I've been faced with this problem before without really finding a solution...
I can offer you an alternative but not perfect!
From a polyline accessory object that I had made to indicate the lengths of polylines.

As you could see in the video after placing the object and setting the step you will have to decompose it, delete the excess lines, unify and adapt the new polylines

Hoping that one day Graphisoft will give us a more efficient solution

https://youtu.be/aLo535xhi1M

Re: Polylines are too dense to magic wand for mesh contour

danielk — Thu, 24 Apr 2025 09:04:29 GMT

Oh, wow, I didn't know polyline accessories were a thing. Seems like exactly the right thing. This is great.

Re: Polylines are too dense to magic wand for mesh contour

Mathias Jonathan — Thu, 24 Apr 2025 09:11:51 GMT

The polyline accessory is hidden by default, you have to modify your menu to show it. Yves also made a must have object to create 3D prism with closed polylines: https://community.graphisoft.com/t5/Modeling/Any-tip-as-how-to-create-multiple-slabs-in-one-go/m-p/595469/highlight/true#M170972

Re: Polylines are too dense to magic wand for mesh contour

danielk — Sun, 27 Apr 2025 16:56:15 GMT

Hi,

Inspired by Yves' clever solution, I made a polyline reduction object similar to his, but using a different algorithm, that should keep the shape of the original more intact, so you wouldn't need to adjust the result after exploding (other than joining the line segments).

Same steps as for Yves' object otherwise. You have one input, which is the number of points you want on your new polyline.

This is a prototype of a prototype, so let me know how it performs, so that I can fix any issues.

Thanks!

Re: Polylines are too dense to magic wand for mesh contour

JeffH — Thu, 24 Apr 2025 19:53:13 GMT

I just tried it out and the contour line i tested on, it worked great.

Once the object was created, I selected it, and exploded it into lines

Then unified, and had 1/3 of the nodes along that single piece of Topo.

Thanks!