Geom2dGcc_Circ2d2TanRad

Dear Pawel,

I haven't used that myself. However, you can have a look at the OC source:
\ros\src\ChFi2d\ChFi2d_Builder.cxx
\ros\src\Geom2dGcc\Geom2dGcc_Circ2d2TanRad.cxx

I use BRepFilletAPI_MakeFillet2d. This is a snippet from my code:

///
/// Adds fillets to a wire.
///
/// The input wire.
/// The output wire with fillets.
/// The array list containing:
/// (0) - x coordinate of the vertex to add the fillet to;
/// (1) - z coordinate of the vertex to add the fillet to;
/// (2) - the radius of the fillet.
/// The input wire is situated in the XZ plane.
/// true if the method succeeds.
/// Otherwise false.
bool shellDocBase::AddFilletsToPlanarWire(
BRepBuilderAPI_MakeWire &wire, BRepBuilderAPI_MakeWire &outputWire,
ArrayList ^ filletsArrayList)
{
if(filletsArrayList == nullptr)
{
TraceWarning("shellDocBase Error. AddFilletsToPlanarWire - ArrayList NULL pointer.");
return false;
}

BRepFilletAPI_MakeFillet2d fillet;
fillet.Init(BRepBuilderAPI_MakeFace(wire.Wire()));

BRepTools_WireExplorer Ex;
TopoDS_Edge firstEdge;
TopoDS_Edge secondEdge;
TopoDS_Vertex vertex;
gp_Pnt point;
gp_Pnt actPoint;
int j = 1;
bool first = true;

int nb = -1;
TopTools_IndexedMapOfShape aMap1;
TopExp::MapShapes(wire, TopAbs_EDGE, aMap1);
nb = aMap1.Extent();

for(Ex.Init(wire); Ex.More(); ) //iterate through edges
{
if(first == true)
{
firstEdge = Ex.Current();
first = false;
}

Ex.Next();

//if the number of edges is odd don't proceed
if(Ex.More() == Standard_False)
break;

secondEdge = Ex.Current();

//get the common vertex of the two edges
TopExp::CommonVertex(firstEdge, secondEdge, vertex);

point = BRep_Tool::Pnt(vertex);

//check if at this edge there is a fillet
for(j = 0; jCount; )
{
actPoint.SetX(System::Double::Parse(filletsArrayList->default[j + 0]->ToString()));
actPoint.SetY(0);
actPoint.SetZ(System::Double::Parse(filletsArrayList->default[j + 1]->ToString()));

if(actPoint.IsEqual(point, Precision::Confusion()) == Standard_True)
{
TraceDebug(" shellDocBase: AddFilletsToPlanarWire - adding fillet.");
fillet.AddFillet(vertex, System::Double::Parse(filletsArrayList->default[j + 2]->ToString()));
break;
}

j +=3;
}

firstEdge = secondEdge;
}

if(fillet.Status() != ChFi2d_IsDone)
{
CString message = "";

switch(fillet.Status())
{
case ChFi2d_NotPlanar:
message = "ChFi2d_NotPlanar";
break;
case ChFi2d_NoFace:
message = "ChFi2d_NoFace";
break;
case ChFi2d_InitialisationError:
message = "ChFi2d_InitialisationError";
break;
case ChFi2d_ParametersError:
message = "ChFi2d_ParametersError";
break;
case ChFi2d_Ready:
message = "ChFi2d_Ready";
break;
case ChFi2d_IsDone:
message = "ChFi2d_IsDone";
break;
case ChFi2d_ComputationError:
message = "ChFi2d_ComputationError";
break;
case ChFi2d_ConnexionError:
message = "ChFi2d_ConnexionError";
break;
case ChFi2d_TangencyError:
message = "ChFi2d_TangencyError";
break;
case ChFi2d_FirstEdgeDegenerated:
message = "ChFi2d_FirstEdgeDegenerated";
break;
case ChFi2d_LastEdgeDegenerated:
message = "ChFi2d_LastEdgeDegenerated";
break;
case ChFi2d_BothEdgesDegenerated:
message = "ChFi2d_BothEdgesDegenerated";
break;
case ChFi2d_NotAuthorized:
message = "ChFi2d_NotAuthorized";
break;
default:
message = "Unknown";
break;
}

TraceError(" shellDocBase Error. AddFilletsToPlanarWire - Fillet status - not done: " + gcnew String(message) + ".");
return false;
}

if(fillet.Shape().IsNull() == Standard_True)
{
TraceError(" shellDocBase Error. AddFilletsToPlanarWire - Fillet shape Null.");
return false;
}

//=====================================
TraceDebug(" shellDocBase: AddFilletsToPlanarWire - consulting fillet result.");
BRepBuilderAPI_MakeWire newWire;
TopTools_IndexedMapOfShape aMap;

TopExp::MapShapes(fillet.Shape(), TopAbs_WIRE, aMap);
if(aMap.Extent() != 1)
{
TraceErrorFormattedStr(" shellDocBase Error. AddFilletsToPlanarWire - multiple/no wires detected: ","%i",".",aMap.Extent());
return false;
}

//add edges to the wire
Ex.Clear();
for(Ex.Init(TopoDS::Wire(aMap(1))); Ex.More(); Ex.Next())
{
newWire.Add(Ex.Current());
}
outputWire = newWire;

return true;
}

Hope it helps.

Good luck!
Pawel