space curve display

Hello everybody, I'd like to display part of the set of edges (or edges or faces) of TopoDS_Shape. The following code works well for vertices cases and faces case.

TopoDS_Compound aCompound;//common faces
BRep_Builder aBuilder;

for(int i=1;i {
if(m_FaceLabel[i]==k1||m_FaceLabel[i]==k2)
{
TopoDS_Face F=TopoDS::Face(m_FaceMap(i));
aBuilder.Add(aCompound,F);
}
}
m_AISFacesPart=new AIS_Shape(aCompound);

for(int i=1;im_VertexMap.Extent();i++)
{
TopoDS_Shape S=m_VertexMap(m_CPMap[k]->m_VertexMap(i));
TopoDS_Vertex V=TopoDS::Vertex(S);
aBuilder.Add(aCompound,V);
}
m_AISVertexPart=new AIS_Shape(aCompound);

But for edges cases, nothing is displayed when using the following code:

for(int i=1;im_EdgeMap.Extent();i++)
{
TopoDS_Shape S=m_EdgeMap(m_CPMap[k]->m_EdgeMap(i));
TopoDS_Edge E=TopoDS::Edge(S);
aBuilder.Add(aCompound,E);
}
m_AISVertexPart=new AIS_Shape(aCompound);

Why? Would someboby give me some suggestions?
btw. If I have a Handle(Geom_Curve), how to convert it into a Handle(AIS_Shape) to display it?

Many thanks!