wrong normal directions by use BRepLProp_SLProps

This is part of my code, and I got some wrong normal directions by use BRepLProp_SLProps，
Can you give me some advice？thanks a lot

for (faceExplorer.Init(aShape, TopAbs_FACE); faceExplorer.More(); faceExplorer.Next())
{

TopLoc_Location loc ;
TopoDS_Face aFace = TopoDS::Face(faceExplorer.Current());
Handle_Poly_Triangulation triFace = BRep_Tool::Triangulation(aFace, loc);
BRepLProp_SLProps theProp(BRepAdaptor_Surface(aFace), 1, Precision::Confusion());

if (triFace.IsNull()) continue;

Standard_Boolean hasNormal = triFace->HasNormals();
Standard_Boolean hasuvNormal = triFace->HasUVNodes();

Standard_Integer l = triFace->Nodes().Length();
Standard_Integer nTriangles = triFace->NbTriangles();

TColgp_Array1OfPnt nodes(1, triFace->NbNodes());
Poly_Array1OfTriangle triangles(1, triFace->NbTriangles());
nodes = triFace->Nodes();
triangles = triFace->Triangles();

BRepAdaptor_Surface S;
S.Initialize(aFace, Standard_False);

for (Standard_Integer i = 1; i <= nTriangles; i++)
{
Poly_Triangle aTriangle = triangles.Value(i);
aTriangle.Get(nVertexIndex1, nVertexIndex2, nVertexIndex3);

vertex1 = nodes.Value(nVertexIndex1).Transformed(loc.Transformation());
vertex2 = nodes.Value(nVertexIndex2).Transformed(loc.Transformation());
vertex3 = nodes.Value(nVertexIndex3).Transformed(loc.Transformation());

gp_Pnt2d theUV1 = triFace->UVNodes().Value(aTriangle(1));
gp_Pnt2d theUV2 = triFace->UVNodes().Value(aTriangle(2));
gp_Pnt2d theUV3 = triFace->UVNodes().Value(aTriangle(3));

positionBuffer.push_back(aiVector3D());
aiVector3D* vt1 = &positionBuffer.back();
vt1->x = vertex1.X();
vt1->y = vertex1.Y();
vt1->z = vertex1.Z();

positionBuffer.push_back(aiVector3D());
aiVector3D* vt2 = &positionBuffer.back();
vt2->x = vertex2.X();
vt2->y = vertex2.Y();
vt2->z = vertex2.Z();

positionBuffer.push_back(aiVector3D());
aiVector3D* vt3 = &positionBuffer.back();
vt3->x = vertex3.X();
vt3->y = vertex3.Y();
vt3->z = vertex3.Z();

// find the normal for the triangle mesh.

gp_Vec V12(vertex1, vertex2);
gp_Vec V13(vertex1, vertex3);
gp_Vec theNormal = V12 ^ V13;
gp_Vec theNormal1 = theNormal;
gp_Vec theNormal2 = theNormal;
gp_Vec theNormal3 = theNormal;
if (theNormal.Magnitude() > Precision::Confusion())
{
theNormal.Normalize();
theNormal1.Normalize();
theNormal2.Normalize();
theNormal3.Normalize();
}

theProp.SetParameters(theUV1.X(), theUV1.Y());
if (theProp.IsNormalDefined())
{
theNormal1 = theProp.Normal();
}

theProp.SetParameters(theUV2.X(), theUV2.Y());
if (theProp.IsNormalDefined())
{
theNormal2 = theProp.Normal();
}

theProp.SetParameters(theUV3.X(), theUV3.Y());
if (theProp.IsNormalDefined())
{
theNormal3 = theProp.Normal();
}

if (aFace.Orientation() == TopAbs_REVERSED)
{
theNormal.Reverse();
theNormal1.Reverse();
theNormal2.Reverse();
theNormal3.Reverse();
}

normalBuffer.push_back(aiVector3D());
aiVector3D* vn1 = &normalBuffer.back();
vn1->x = theNormal1.X();
vn1->y = theNormal1.Y();
vn1->z = theNormal1.Z();

normalBuffer.push_back(aiVector3D());
aiVector3D* vn2 = &normalBuffer.back();
vn2->x = theNormal2.X();
vn2->y = theNormal2.Y();
vn2->z = theNormal2.Z();

normalBuffer.push_back(aiVector3D());
aiVector3D* vn3 = &normalBuffer.back();
vn3->x = theNormal3.X();
vn3->y = theNormal3.Y();
vn3->z = theNormal3.Z();

}
}