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Semicircular Mesh

Anonymous
Not applicable
Hello,
I have run into something strange with the mesh tool.
The attached image shows a semicircle drawn with arcs and lines.
Above that is a mesh made by tracing the figure made with arcs and lines.
When I go to the 3D window to view the mesh I get a warning
saying "Invalid polygon, self-intersection or hole intersects boundary".
Nothing appears in the 3D window.
If I trace the same figure using the slab tool or the roof tool and
go to the 3D window I get no warning and the slab or roof
show in 3D.
If I make an object out of the mesh using save selection as GDL Object
and open the objects 3D script and check script I get an OK but
if I go to the 3D view I get an error message saying
"Invalid curve definition at line......" and the 3D image fails to process.
I have tried this in both AC 8.1 and AC 9.
Would someone verify this behavior and perhaps
suggest a way to make such a mesh shape work.
I know that if I make the included angle one degree less than 180°
or make the inner radius 1/64" less than 10'-0" the error does not occur.
This work around is not satisfactory.
Thank you,
Peter Devlin
25 REPLIES 25
Anonymous
Not applicable
Peter wrote:
I found the same thing with a slab with a concave quarter arc cut into it.
Peter Devlin
You mean that apears "error" warning for slab too
ok, that's can really be, because the same methods for all shapes. Difference is only that some times slabs with non-correct coords are generated without error, but not Mashes!

I think the the problem is in analytic method, when AC creats some shape.
Anonymous
Not applicable
Hello Z.Bauer,
I did not get an error and the slab processed ok.
I focused in and noticed this odd hook at one corner.
Peter Devlin
Ed_Brown
Graphisoft Alumni
Graphisoft Alumni
Peter and Z.Bauer,

It appears you two have run across some weaknesses in ArchiCAD.

Peter’s mesh entry method is indeed novel. I tried it a couple of times but it always confused ArchiCAD. I couldn’t even get a mesh let alone the one you describe. In the end I added the mesh using the mesh entry tools and had no trouble. The main point here is that, you can make a semi-circular arch that is 180 degrees and 10’ in diameter/radius -- or any size for that matter. You just have to use the mesh drawing tools. The problem here is that in the process of stretching lines and moving nodes across each other ArchiCAD loses track of what is inside and what is outside the polygon (it is also possible that a new node is created that creates a self-intersection –but I did not witness this). No doubt, very interesting!

Z.Bauer ran into a different weakness. Three dimensional bodies that are self intersecting pose a problem to ArchiCAD (and for that fact most 3d editing tools). In general, 3d editing tools use algorithms that identify these self intersecting parts and correct for them. The protrusion that Z.Bauer mentions is the point of self intersection. The mass routine needs to have the same regularization algorithm that the extrude, slab and poly have. The workaround here is to correct by hand for the self intersection in the script and the mass function will work.

Peter it would be helpful if you could make a pln that illustrates precisely the steps you take. I would like to see that this entry method be studied and the error corrected soon.

Z.Bauer I have entered the error you noted and I presume it will be corrected soon. Do you too have a method for how you created the set of points?

Thank you,

Ed Brown
Graphisoft Technical Support
Anonymous
Not applicable
Ed,
I will have to get the .pln file to you via David Taur because it is to large
to attach to a post here.
Thank you,
Peter Devlin
Anonymous
Not applicable
Ed wrote:
Z.Bauer I have entered the error you noted and I presume it will be corrected soon. Do you too have a method for how you created the set of points?
Hello Ed,

thank's, I hope GS solves this problem soon.

You find all in this attached .pla file.
Anonymous
Not applicable
I just checked in AC 12 and this problem, two versions later, is still with us.
Peter Devlin