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?
Graphisoft Technical Support