BRepProj_Projection of a wire which is already lying on the face => does not work

Hi,

I have a simple wire (line) and a face. Now I try to project the wire onto the face (BRepProj_Projection). "IsDone" returns true and the resulting wire is correct. Wonderful.

But... sometimes "IsDone" returns false. IMHO this occurs, if the wire already lies on the face. So I tried to force this situation by projecting the result from the first projection on the same face. If I use the appended face.brep, the second projection returns IsDone=false.

How can I distinguish between
"the wire cannot be projected, because there is no result"
and
"the wire cannot be projected, because it already lies on the face"
?

BTW: if I use a plane for the face, the second projection returns IsDone=true. :-/

Here is my code (OCCT 6.6.0):

Handle_V3d_View view = ui.qOCViewer->getV3DView();
Handle_AIS_InteractiveContext context = ui.qOCViewer->getContext();
context->SetDisplayMode(AIS_Shaded);

gp_Pnt p1(382, -300, 100);
gp_Pnt p2(382, 300, 100);
gp_Pnt pMid = p1.Translated(gp_Vec(p1, p2).Scaled(0.5));
addToView(pMid);
TopoDS_Edge edge = BRepBuilderAPI_MakeEdge(p1, p2);
context->Display(new AIS_Shape(edge));

gp_Dir direction(0,0,1);

TopoDS_Face face;
bool usePlane = false;
if (usePlane)
{
gp_Pnt pnt = pMid.Translated(gp_Vec(0,0,-100));
gp_Pln plane(pnt, direction);
face = BRepBuilderAPI_MakeFace(plane, -50, 50, -50, 50);
}
else
{
BRep_Builder builder;
TopoDS_Shape importedShape;
Standard_Boolean ok = BRepTools::Read(importedShape, "face.brep", builder);
if (!ok )
{
throw std::exception("Cannot load face");
}
for(TopExp_Explorer ex(importedShape, TopAbs_FACE, TopAbs_SHAPE); ex.More(); ex.Next())
{
face = TopoDS::Face(ex.Current());
}
}
if (face.IsNull())
{
throw std::exception("face is null");
}
context->Display(new AIS_Shape(face));

bool done1 = false;
bool done2 = false;
TopoDS_Shape resultShape;
BRepProj_Projection projector1(edge, face, direction);
if (projector1.IsDone())
{
done1 = true;
resultShape = projector1.Current();// Shape();
}
else
{
direction.Reverse();
BRepProj_Projection projector2(edge, face, direction);
if (projector2.IsDone())
{
done2 = true;
resultShape = projector2.Current();// Shape();
}
}
log(QString("done1 == %0; done2 == %1").arg(done1).arg(done2));
if (done1 || done2)
{
context->Display(new AIS_Shape(resultShape));
}

bool done3 = false;
bool done4 = false;
TopoDS_Shape resultShape2;
BRepProj_Projection projector3(resultShape, face, direction);
if (projector3.IsDone())
{
done3 = true;
resultShape2 = projector3.Current();// Shape();
}
else
{
direction.Reverse();
BRepProj_Projection projector4(resultShape, face, direction);
if (projector4.IsDone())
{
done4 = true;
resultShape2 = projector4.Current();// Shape();
}
}
log(QString("done3 == %0; done4 == %1").arg(done3).arg(done4));
if (done3 || done4)
{
context->Display(new AIS_Shape(resultShape2));
}