How to differentiate between a circle and an arc

[bioan]

How can I differentiate between an full circle and an arc of the same support circle?
I'm trying to cycle through the elements of a TopoDS_Shape of type TopAbs_COMPOUND.
Everything just work fine using the below code:

double u0, u1;
Handle(Geom_Curve) Curve;
TopoDS_Edge Edge;
Curve = BRep_Tool::Curve(Edge, u0, u1);

GeomAdaptor_Curve brepCurveAdaptor(Curve);
GeomAbs_CurveType curveType = brepCurveAdaptor.GetType();
switch (curveType)
{
   case GeomAbs_Circle:
   {
      if (Curve->IsClosed())
      {
      // here the code always runs no matter is an arc or a circle
      }
   }
}

I can use u0 and u1 values to decide it. If 0 to 2*PI - is a circle, otherwise if 0 to <2*PI is an arc.
My question is whether there is a more elegant method (as it should have been IsClosed() ) than the raw checking of the values of the parameters u0 and u1.
Thank you!

 

[Jonathan]

Standard_Boolean Geom_Circle::IsClosed () const { return Standard_True; }

I am not sure but wouldn't an arc be a Geom_TrimmedCurve?

 

[Quaoar]

I can use u0 and u1 values to decide it. If 0 to 2*PI - is a circle, otherwise if 0 to <2*PI is an arc.

That would also be my choice

 

[bioan]

Standard_Boolean Geom_Circle::IsClosed () const { return Standard_True; }

I am not sure but wouldn't an arc be a Geom_TrimmedCurve?

Hi Jonathan! All I have as input data is an array of Geom_Curve. I do not know when or if I need to check these Geom_Curve if some of them are of Geom_TrimmedCurve type. I assumed that IsClosed () might help, but unfortunately, regardless of whether it is a arc or a circle, this function returns true all the time.

 

[bioan]

That would also be my choice

Thank you!

 

[Quaoar]

I assumed that IsClosed () might help, but unfortunately, regardless of whether it is a arc or a circle, this function returns true all the time.

I would assume it's a purely geometric check. What you could also try is ShapeAnalysis_Edge::IsClosed3d(). It has an early exit condition on !IsClosed() and then checks the vertices. For a closed arc (and any closed edge), there should presumably be a shared vertex.

 

[bioan]

I would assume it's a purely geometric check. What you could also try is ShapeAnalysis_Edge::IsClosed3d(). It has an early exit condition on !IsClosed() and then checks the vertices. For a closed arc (and any closed edge), there should presumably be a shared vertex.

Excellent info!!
Yes, the verification is purely geometric. I managed to differentiate using the parameter values u0 and u1. It seems to work just perfectly!
Thank you very much!!
All the best!
Ioan

 

[blobfish]

Excellent info!!
Yes, the verification is purely geometric. I managed to differentiate using the parameter values u0 and u1. It seems to work just perfectly!
Thank you very much!!
All the best!
Ioan

The parameter range will describe a circle not necessarily (0, 2*PI) parameters. Something like this is legit.

BRepBuilderAPI_MakeEdge em(gp_Circ(gp_Ax2(), 1.0), M_PI, 3.0 * M_PI);
assert(em.IsDone());
TopoDS_Edge anEdge = em;
assert(BRep_Tool::IsClosed(anEdge));

In addition with parameters, you need to compensate for numerical error. So you get into something like std::fabs(lastParameter - firstParameter - 2*M_PI) <= Precision:: PConfusion. And that doesn't consider any vertex tolerances. My point: Use TopoDS_Shape and relative algos whenever possible and let occt take care of the minutia underneath.

 

[bioan]

The parameter range will describe a circle not necessarily (0, 2*PI) parameters. Something like this is legit.

BRepBuilderAPI_MakeEdge em(gp_Circ(gp_Ax2(), 1.0), M_PI, 3.0 * M_PI);
assert(em.IsDone());
TopoDS_Edge anEdge = em;
assert(BRep_Tool::IsClosed(anEdge));

In addition with parameters, you need to compensate for numerical error. So you get into something like std::fabs(lastParameter - firstParameter - 2*M_PI) <= Precision:: PConfusion. And that doesn't consider any vertex tolerances. My point: Use TopoDS_Shape and relative algos whenever possible and let occt take care of the minutia underneath.

Thank you very much for your observations!!