[Gmsh] Can arcs be exactly pi radians?

Christophe Geuzaine cgeuzaine at ulg.ac.be
Fri Aug 19 18:28:49 CEST 2016

> On 14 Aug 2016, at 16:49, Jim Monte <jim.gmsh at gmail.com> wrote:
> Hi All,
> I am very new here. I need to make many circles. The documentation says in section 5.1.2
> "Circle ( expression ) = { expression, expression, expression };
> Creates a circle arc (strictly) smaller than Pi..."
> This would mean at least three perimeter points would be needed to make each circle. I tried with two points making arcs exactly pi radians each. They display properly, but I am wondering what problems I would have making all of the circles with two points (and a center point) instead of more. Thanks for any information.

The little internal Gmsh CAD engine is indeed limited to circle arcs < Pi. When = Pi the specification of the plane in which the circle lives cannot be computed in a univoque manner.

(It's not documented but you can actually specify the plane by its normal vector explicitly as follows: Circle(num) = {p1,p2,p3} Plane {nx,ny,nz};)


> Jim
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Prof. Christophe Geuzaine
University of Liege, Electrical Engineering and Computer Science 

Tetrahedron V, July 4-5 2016: http://tetrahedron.montefiore.ulg.ac.be
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