gp_Pnt ViewCalculations::convert2DPointTo3DPoint(Standard_Real x, Standard_Real y, Handle(V3d_View) aView)
{
    V3d_Coordinate XEye,YEye,ZEye,XAt,YAt,ZAt;
    aView->Eye(XEye,YEye,ZEye);
    aView->At(XAt,YAt,ZAt);
    gp_Pnt EyePoint(XEye,YEye,ZEye);
    gp_Pnt AtPoint(XAt,YAt,ZAt);

    gp_Vec EyeVector(EyePoint,AtPoint);
    gp_Dir EyeDir(EyeVector);

    gp_Pln PlaneOfTheView = gp_Pln(AtPoint,EyeDir);
    Standard_Real X,Y,Z;
    aView->Convert(int(x),int(y),X,Y,Z);
    gp_Pnt ConvertedPoint(X,Y,Z);
    gp_Pnt2d ConvertedPointOnPlane = ProjLib::Project(PlaneOfTheView,ConvertedPoint);

    gp_Pnt ResultPoint = ElSLib::Value(ConvertedPointOnPlane.X(),
                                       ConvertedPointOnPlane.Y(),
                                       PlaneOfTheView);

    return ResultPoint;
}

gp_Pnt ViewCalculations::convert2DpointTo3DPointOnPlane(Standard_Real x, Standard_Real y, Handle(V3d_View) view)
{
    Standard_Real Xp = x, Yp = y;
    Standard_Real Xv, Yv, Zv;
    Standard_Real Vx, Vy, Vz;

    gp_Pln aPlane(view->Viewer()->PrivilegedPlane());
    view->Convert( Xp, Yp, Xv, Yv, Zv );
    view->Proj( Vx, Vy, Vz );

    gp_Lin aLine(gp_Pnt(Xv, Yv, Zv), gp_Dir(Vx, Vy, Vz));
    IntAna_IntConicQuad theIntersection (aLine, aPlane, Precision::Angular());
    if (theIntersection.IsDone()) {
        if (!theIntersection.IsParallel()) {
            if (theIntersection.NbPoints() > 0) {
                gp_Pnt theSolution(theIntersection.Point(1));
                return gp_Pnt(theSolution.X(), theSolution.Y(), theSolution.Z());
//                if (usePrecision)
//                {
//                    X = (X < 0. ? -1 : (X > 0. ? 1 : 0.)) * floor((abs(X)) / myPrecision) * myPrecision;
//                    Y = (Y < 0. ? -1 : (Y > 0. ? 1 : 0.)) * floor((abs(Y)) / myPrecision) * myPrecision;
//                    Z = (Z < 0. ? -1 : (Z > 0. ? 1 : 0.)) * floor((abs(Z)) / myPrecision) * myPrecision;
//                }
            }
        }
    }
}