diff --git a/Common/operator_base.h b/Common/operator_base.h
index cad69d8..e01b696 100644
--- a/Common/operator_base.h
+++ b/Common/operator_base.h
@@ -69,8 +69,20 @@ public:
 	*/
 	virtual double GetEdgeArea(int ny, const unsigned int pos[3], bool dualMesh = false) const =0;
 
-	//! Snap the given coodinates to mesh indices
-	virtual bool SnapToMesh(const double* coord, unsigned int* uicoord, bool lower=false, bool* inside=NULL) const =0;
+	//! Snap the given coodinates to mesh indices, return box dimension
+	virtual bool SnapToMesh(const double* coord, unsigned int* uicoord, bool dualMesh=false, bool* inside=NULL) const =0;
+
+	//! Snap a given box to the operator mesh, uiStart will be always <= uiStop
+	/*!
+	  \param[in] start the box-start coorindate
+	  \param[in] stop  the box-stopt coorindate
+	  \param[out] uiStart the snapped box-start coorindate index
+	  \param[out] uiStop the snapped box-stop coorindate index
+	  \param[in] dualMesh snap to main or dual mesh (default is main mesh)
+	  \param[in] SnapMethod Snapping method, 0=snap to closest line, 1/(2)=snap such that given box is inside (outside) the snapped lines
+	  \return returns the box dimension or -1 if box is not inside the simulation domain
+	  */
+	virtual int SnapBox2Mesh(const double* start, const double* stop, unsigned int* uiStart, unsigned int* uiStop, bool dualMesh=false, int SnapMethod=0, bool* bStartIn=NULL, bool* bStopIn=NULL) const =0;
 
 	//! Set the boundary conditions
 	virtual void SetBoundaryCondition(int* BCs) {for (int n=0; n<6; ++n) m_BC[n]=BCs[n];}
diff --git a/FDTD/operator.cpp b/FDTD/operator.cpp
index 545cdeb..cf3a26d 100644
--- a/FDTD/operator.cpp
+++ b/FDTD/operator.cpp
@@ -16,6 +16,7 @@
 */
 
 #include <fstream>
+#include <algorithm>
 #include "operator.h"
 #include "engine.h"
 #include "extensions/operator_extension.h"
@@ -253,6 +254,69 @@ bool Operator::SnapToMesh(const double* dcoord, unsigned int* uicoord, bool dual
 	return ok;
 }
 
+int Operator::SnapBox2Mesh(const double* start, const double* stop, unsigned int* uiStart, unsigned int* uiStop, bool dualMesh, int SnapMethod, bool* bStartIn, bool* bStopIn) const
+{
+	double l_start[3], l_stop[3];
+	for (int n=0;n<3;++n)
+	{
+		l_start[n] = fmin(start[n],stop[n]);
+		l_stop[n] = fmax(start[n], stop[n]);
+		double min = GetDiscLine(n,0);
+		double max = GetDiscLine(n,GetNumberOfLines(n)-1);
+		if ( ((l_start[n]<min) && (l_stop[n]<min)) || ((l_start[n]>max) && (l_stop[n]>max)) )
+		{
+			return -1;
+		}
+	}
+
+	SnapToMesh(l_start, uiStart, dualMesh, bStartIn);
+	SnapToMesh(l_stop, uiStop, dualMesh, bStopIn);
+	int iDim = 0;
+
+	if (SnapMethod==0)
+	{
+		for (int n=0;n<3;++n)
+			if (uiStop[n]>uiStart[n])
+				++iDim;
+		return iDim;
+	}
+	else if (SnapMethod==1)
+	{
+		for (int n=0;n<3;++n)
+		{
+			if (uiStop[n]>uiStart[n])
+			{
+				if ((GetDiscLine( n, uiStart[n], dualMesh ) > l_start[n]) && (uiStart[n]>0))
+					--uiStart[n];
+				if ((GetDiscLine( n, uiStop[n], dualMesh ) < l_stop[n]) && (uiStop[n]<GetNumberOfLines(n)-1))
+					++uiStop[n];
+			}
+			if (uiStop[n]>uiStart[n])
+				++iDim;
+		}
+		return iDim;
+	}
+	else if (SnapMethod==2)
+	{
+		for (int n=0;n<3;++n)
+		{
+			if (uiStop[n]>uiStart[n])
+			{
+				if ((GetDiscLine( n, uiStart[n], dualMesh ) < l_start[n]) && (uiStart[n]<GetNumberOfLines(n)-1))
+					++uiStart[n];
+				if ((GetDiscLine( n, uiStop[n], dualMesh ) > l_stop[n]) && (uiStop[n]>0))
+					--uiStop[n];
+			}
+			if (uiStop[n]>uiStart[n])
+				++iDim;
+		}
+		return iDim;
+	}
+	else
+		cerr << "Operator::SnapBox2Mesh: Unknown snapping method!" << endl;
+	return -1;
+}
+
 struct Operator::Grid_Path Operator::FindPath(double start[], double stop[])
 {
 	struct Grid_Path path;
@@ -1205,18 +1269,8 @@ bool Operator::Calc_LumpedElements()
 				unsigned int uiStart[3];
 				unsigned int uiStop[3];
 				// snap to the native coordinate system
-				SnapToMesh(box->GetStartCoord()->GetNativeCoords(),uiStart);
-				SnapToMesh(box->GetStopCoord()->GetNativeCoords(),uiStop);
-
-				for (int n=0;n<3;++n)
-				{
-					if (uiStop[n]<uiStart[n])
-					{
-						unsigned int help = uiStart[n];
-						uiStart[n]=uiStop[n];
-						uiStop[n]=help;
-					}
-				}
+				if (Operator::SnapBox2Mesh(box->GetStartCoord()->GetNativeCoords(), box->GetStopCoord()->GetNativeCoords(), uiStart, uiStop)<=0)
+					return false;
 
 				if (uiStart[ny]==uiStop[ny])
 				{
diff --git a/FDTD/operator.h b/FDTD/operator.h
index 676b6ef..8d83810 100644
--- a/FDTD/operator.h
+++ b/FDTD/operator.h
@@ -120,8 +120,12 @@ public:
 
 	virtual unsigned int SnapToMeshLine(int ny, double coord, bool &inside, bool dualMesh=false) const;
 
+	//! Snap the given coodinates to mesh indices
 	virtual bool SnapToMesh(const double* coord, unsigned int* uicoord, bool dualMesh=false, bool* inside=NULL) const;
 
+	//! Snap a given box to the FDTD mesh
+	virtual int SnapBox2Mesh(const double* start, const double* stop, unsigned int* uiStart, unsigned int* uiStop, bool dualMesh=false, int SnapMethod=0, bool* bStartIn=NULL, bool* bStopIn=NULL) const;
+
 	virtual void AddExtension(Operator_Extension* op_ext);
 	virtual size_t GetNumberOfExtentions() const {return m_Op_exts.size();}
 	virtual Operator_Extension* GetExtension(size_t index) const {return m_Op_exts.at(index);}