diff --git a/src/phasicFlow/fileSystem/fileSystem.cpp b/src/phasicFlow/fileSystem/fileSystem.cpp
index 3423ac0b..a4275f56 100644
--- a/src/phasicFlow/fileSystem/fileSystem.cpp
+++ b/src/phasicFlow/fileSystem/fileSystem.cpp
@@ -33,7 +33,6 @@ bool pFlow::fileSystem::checkFileName(const word& name)
 		"Invalid file name supplied " << name <<
 		"the following characters are not allowd: " <<
 		notPermittedCharsFile << endl;
-		fatalExit;
 		return false;
 	}
 
@@ -57,9 +56,9 @@ pFlow::fileSystem::fileSystem( const word& dir, const word& file)
 {
 	isDir_ = file.empty();
 
-	if( !isDir_) 
+	if( !isDir_ && !checkFileName(file)) 
 	{
-		checkFileName(file);
+		fatalExit;
 	}
 
 	try
@@ -240,7 +239,10 @@ pFlow::fileSystem pFlow::fileSystem::operator()
 
 void pFlow::fileSystem::operator += (const word& fileName)
 {
-	checkFileName(fileName);
+	if(!checkFileName(fileName))
+	{
+		fatalExit;
+	}
 
 	if( isDir())
 	{
diff --git a/src/phasicFlow/streams/Fstream/fileStream.cpp b/src/phasicFlow/streams/Fstream/fileStream.cpp
index a577d83c..cbd14ae8 100755
--- a/src/phasicFlow/streams/Fstream/fileStream.cpp
+++ b/src/phasicFlow/streams/Fstream/fileStream.cpp
@@ -70,13 +70,30 @@ void pFlow::fileStream::openOutFile
 	
 	if(binary_)
 	{
-		outStream_ = makeUnique< std::ofstream>(
+		if(append_)
+		{
+			outStream_ = makeUnique< std::ofstream>(
+			path.wordPath(), std::ios_base::out| std::ios::binary|std::ios::app);
+		}
+		else
+		{
+			outStream_ = makeUnique< std::ofstream>(
 			path.wordPath(), std::ios_base::out| std::ios::binary);
+		}
 	}
 	else
-		outStream_ = makeUnique< std::ofstream>(
+	{
+		if(append_)
+		{
+			outStream_ = makeUnique< std::ofstream>(
+			path.wordPath(), std::ios_base::out|std::ios::app);
+		}
+		else
+		{
+			outStream_ = makeUnique< std::ofstream>(
 			path.wordPath(), std::ios_base::out);
-
+		}
+	}
 
 	if(!outStream_->is_open())
 	{
@@ -103,12 +120,14 @@ pFlow::fileStream::fileStream
 (
 	const fileSystem& path,
 	bool outStream,
-	bool binary
+	bool binary,
+	bool append
 )
 :
 	inStream_(nullptr),
 	outStream_(nullptr),
-	binary_(binary)
+	binary_(binary),
+	append_(append)
 {
 
 	if(outStream)
diff --git a/src/phasicFlow/streams/Fstream/fileStream.hpp b/src/phasicFlow/streams/Fstream/fileStream.hpp
index 0cf6f34b..670c13e3 100755
--- a/src/phasicFlow/streams/Fstream/fileStream.hpp
+++ b/src/phasicFlow/streams/Fstream/fileStream.hpp
@@ -52,6 +52,8 @@ protected:
 
 	bool binary_ = false;
 	
+	bool append_ = false;
+
 	/// open input file
 	void openInFile(const fileSystem& path);
 	
@@ -66,7 +68,7 @@ public:
 	//// - Constructors
 
 		/// From file path and input type and format. 
-		fileStream( const fileSystem& path, bool outStream = false, bool binary = false);
+		fileStream( const fileSystem& path, bool outStream = false, bool binary = false, bool append = false);
 		
 		/// No copy
 		fileStream(const fileStream&)= delete;
diff --git a/src/phasicFlow/streams/Fstream/oFstream.cpp b/src/phasicFlow/streams/Fstream/oFstream.cpp
index 54e1606a..95da62ae 100755
--- a/src/phasicFlow/streams/Fstream/oFstream.cpp
+++ b/src/phasicFlow/streams/Fstream/oFstream.cpp
@@ -22,9 +22,9 @@ Licence:
 #include "oFstream.hpp"
 
 
-pFlow::oFstream::oFstream (const fileSystem& path, bool binary)
+pFlow::oFstream::oFstream (const fileSystem& path, bool binary, bool append)
 :
-	fileStream(path, true, binary),
+	fileStream(path, true, binary, append),
 	Ostream
   ( 
     fileStream::outStream(), 
diff --git a/src/phasicFlow/streams/Fstream/oFstream.hpp b/src/phasicFlow/streams/Fstream/oFstream.hpp
index 3092b2ca..1b1699f6 100755
--- a/src/phasicFlow/streams/Fstream/oFstream.hpp
+++ b/src/phasicFlow/streams/Fstream/oFstream.hpp
@@ -45,7 +45,7 @@ public:
 	//// - Constructors
 	
 	/// From file path and format 
-	oFstream (const fileSystem& path, bool binary = false);
+	oFstream (const fileSystem& path, bool binary = false, bool append = false);
 
 	/// No copy constructor
 	oFstream( const oFstream& src) = delete;
diff --git a/utilities/Utilities/vtkFile/vtkFile.cpp b/utilities/Utilities/vtkFile/vtkFile.cpp
index fe0755f4..dc4b9039 100755
--- a/utilities/Utilities/vtkFile/vtkFile.cpp
+++ b/utilities/Utilities/vtkFile/vtkFile.cpp
@@ -21,11 +21,14 @@ Licence:
 
 #include "vtkFile.hpp"
 
-bool pFlow::vtkFile::openStream()
+bool pFlow::vtkFile::openStream(bool wHeader)
 {
-	oStream_ = makeUnique<oFstream>( fileName() );
+	oStream_ = makeUnique<oFstream>( fileName(), false, append_ );
 	if( !oStream_ )return false;
-	return writeHeader();
+	if(wHeader)
+		return writeHeader();
+	else
+		return true;
 }
 
 bool pFlow::vtkFile::vtkFile::writeHeader()
@@ -49,15 +52,17 @@ pFlow::vtkFile::vtkFile
 (
 	const fileSystem dir,
 	const word& bName,
-	real time
+	real time,
+	bool append
 )
 :
 	dirPath_(dir),
 	baseName_(bName),
-	time_(time)
+	time_(time),
+	append_(append)
 {
 
-	if(!openStream())
+	if(!openStream(!append))
 	{
 		fatalErrorInFunction <<
 		"  error in creating vtkFile "<<fileName()<<endl;
diff --git a/utilities/Utilities/vtkFile/vtkFile.hpp b/utilities/Utilities/vtkFile/vtkFile.hpp
index 8c4cab36..9d3ad79e 100755
--- a/utilities/Utilities/vtkFile/vtkFile.hpp
+++ b/utilities/Utilities/vtkFile/vtkFile.hpp
@@ -40,15 +40,21 @@ protected:
 
 	real  	   time_ = 0.0;
 
+	bool		append_=false;
+
 	uniquePtr<oFstream>  oStream_= nullptr;
 
-	bool openStream();
+	bool openStream(bool wHeader);
 
 	virtual bool writeHeader();
 
 public:
 
-	vtkFile(const fileSystem dir, const word& bName, real time);
+	vtkFile(
+		const fileSystem dir, 
+		const word& bName, 
+		real time,
+		bool append = false);
 
 	virtual ~vtkFile() = default;
 
@@ -56,7 +62,7 @@ public:
 	{
 		if(!oStream_)
 		{
-			if(!openStream())
+			if(!openStream(!append_))
 			{
 				fatalErrorInFunction<<
 				"  error in opening vtkFile "<< fileName() <<endl;
diff --git a/utilities/pFlowToVTK/CMakeLists.txt b/utilities/pFlowToVTK/CMakeLists.txt
index 15f37471..a79a7128 100644
--- a/utilities/pFlowToVTK/CMakeLists.txt
+++ b/utilities/pFlowToVTK/CMakeLists.txt
@@ -1,6 +1,7 @@
 
 set(source_files 
 pointFieldToVTK.cpp
+triSurfaceFieldToVTK.cpp
 pFlowToVTK.cpp 
 #geometric.cpp 
 )
diff --git a/utilities/pFlowToVTK/geometric.cpp b/utilities/pFlowToVTK/geometric.cpp
deleted file mode 100755
index b7afbdda..00000000
--- a/utilities/pFlowToVTK/geometric.cpp
+++ /dev/null
@@ -1,87 +0,0 @@
-/*------------------------------- phasicFlow ---------------------------------
-      O        C enter of
-     O O       E ngineering and
-    O   O      M ultiscale modeling of
-   OOOOOOO     F luid flow       
-------------------------------------------------------------------------------
-  Copyright (C): www.cemf.ir
-  email: hamid.r.norouzi AT gmail.com
-------------------------------------------------------------------------------  
-Licence:
-  This file is part of phasicFlow code. It is a free software for simulating 
-  granular and multiphase flows. You can redistribute it and/or modify it under
-  the terms of GNU General Public License v3 or any other later versions. 
- 
-  phasicFlow is distributed to help others in their research in the field of 
-  granular and multiphase flows, but WITHOUT ANY WARRANTY; without even the
-  implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
-
------------------------------------------------------------------------------*/
-
-
-#include "geometric.hpp"
-
-
-template<>
-bool pFlow::dataToVTK( vtkFile& vtk, const triSurface& surface )
-{
-	
-
-	auto nP = surface.numPoints();
-	auto hPoints = surface.points().hostVector();
-
-	vtk() << "DATASET POLYDATA" << endl;
-	vtk() << "POINTS " << nP << " float" << endl;
-
-
-	for ( auto i=0; i<nP; i++ )
-	{
-		vtk() << hPoints[i].x()  << " " << hPoints[i].y() << " " << hPoints[i].z() << endl;
-		if (!vtk) return false;
-	}
-
-	auto nV = surface.numTriangles();
-	auto hVertices = surface.vertices().hostVector();
-
-	vtk() << "POLYGONS " << nV << "  " << 4*nV << endl;
-
-	for(auto i=0; i<nV; i++)
-	{
-		vtk()<< 3 <<" "<< hVertices[i].x() << " " << hVertices[i].y() <<" "<<hVertices[i].z()<<endl;
-		if (!vtk) return false;
-	}
-
-	return true;
-} 
-
-template<>
-bool pFlow::dataToVTK( vtkFile& vtk, const multiTriSurface& surface )
-{
-
-	auto nP = surface.numPoints();
-	auto hPoints = surface.points().hostVector();
-
-	vtk() << "DATASET POLYDATA" << endl;
-	vtk() << "POINTS " << nP << " float" << endl;
-
-
-	for ( auto i=0; i<nP; i++ )
-	{
-		vtk() << hPoints[i].x()  << " " << hPoints[i].y() << " " << hPoints[i].z() << endl;
-		if (!vtk) return false;
-	}
-
-	auto nV = surface.numTriangles();
-	auto hVertices = surface.vertices().hostVector();
-
-	vtk() << "POLYGONS " << nV << "  " << 4*nV << endl;
-
-	for(auto i=0; i<nV; i++)
-	{
-		vtk()<< 3 <<" "<< hVertices[i].x() << " " << hVertices[i].y() <<" "<<hVertices[i].z()<<endl;
-		if (!vtk) return false;
-	}
-
-	return true;
-
-}
diff --git a/utilities/pFlowToVTK/geometric.hpp b/utilities/pFlowToVTK/geometric.hpp
deleted file mode 100755
index 3c1a4313..00000000
--- a/utilities/pFlowToVTK/geometric.hpp
+++ /dev/null
@@ -1,78 +0,0 @@
-/*------------------------------- phasicFlow ---------------------------------
-      O        C enter of
-     O O       E ngineering and
-    O   O      M ultiscale modeling of
-   OOOOOOO     F luid flow       
-------------------------------------------------------------------------------
-  Copyright (C): www.cemf.ir
-  email: hamid.r.norouzi AT gmail.com
-------------------------------------------------------------------------------  
-Licence:
-  This file is part of phasicFlow code. It is a free software for simulating 
-  granular and multiphase flows. You can redistribute it and/or modify it under
-  the terms of GNU General Public License v3 or any other later versions. 
- 
-  phasicFlow is distributed to help others in their research in the field of 
-  granular and multiphase flows, but WITHOUT ANY WARRANTY; without even the
-  implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
-
------------------------------------------------------------------------------*/
-
-
-#ifndef __geometric_hpp__
-#define __geometric_hpp__ 
-
-#include "vtkFile.hpp"
-#include "triSurface.hpp"
-#include "multiTriSurface.hpp"
-#include "IOobject.hpp"
-
-namespace pFlow
-{
-
-
-template<typename ObjType>
-bool geomObjectToVTK(IOfileHeader& header, real time, fileSystem destPath, word bName)
-{
-
-	if( ObjType::TYPENAME() != header.objectType() )return false;
-
-	auto ioObjPtr = IOobject::make<ObjType>(header);
-
-	auto& data = ioObjPtr().template getObject<ObjType>();
-
-	vtkFile vtk(destPath, bName, time);
-
-	if(!vtk) return false;
-
-	REPORT(1)<<"Converting geometry to vtk."<<endREPORT;
-
-	if(!dataToVTK(vtk, data) )
-	{
-		fatalErrorInFunction<<
-		"  error in writing object "<<ioObjPtr().typeName() << " to folder " << destPath<<endl;
-		fatalExit;
-	}
-	
-	return true;
-}
-
-template<typename Type>
-bool dataToVTK(vtkFile& vtk, const Type& dataEntity)
-{
-	fatalErrorInFunction<<
-	"not implemented function!";
-	fatalExit;
-	return false;
-}
-
-template<>
-bool dataToVTK( vtkFile& vtk, const triSurface& surface );
-
-template<>
-bool dataToVTK( vtkFile& vtk, const multiTriSurface& surface );
-
-
-}
-
-#endif //__geometric_hpp__
diff --git a/utilities/pFlowToVTK/pFlowToVTK.cpp b/utilities/pFlowToVTK/pFlowToVTK.cpp
index be53c75d..44cc6ed8 100755
--- a/utilities/pFlowToVTK/pFlowToVTK.cpp
+++ b/utilities/pFlowToVTK/pFlowToVTK.cpp
@@ -26,7 +26,7 @@ Licence:
 #include "Vectors.hpp"
 #include "phasicFlowKokkos.hpp"
 #include "pointFieldToVTK.hpp"
-//#include "triSurfaceFieldToVTK.hpp"
+#include "triSurfaceFieldToVTK.hpp"
 //#include "readControlDict.hpp"
 
 
@@ -60,10 +60,10 @@ int main(int argc, char** argv )
 		"path");
 	
 	bool separateSurfaces = false;
-	cmds.addOption(
+	cmds.add_flag(
 		"-s,--separate-surfaces",
 		separateSurfaces,
-		"surfaces in the geometry are converted separatedly");
+		"use this when you want to have sub-surfaces in separate files");
 
 	wordVector fields;
 	bool 			 allFields = true;
@@ -117,15 +117,16 @@ int main(int argc, char** argv )
 		if( !validRange.isMember( folders.time() ) )continue;
 		
 		output<< "time: " << Cyan_Text( folders.time() )<<" s" <<endl;
-		/*if(!noGoem)
+		if(!noGoem)
 		{	
-			fileSystem geomFolder = folders.folder()/geometryFolder__;
-			if(!pFlow::TSFtoVTK::convertTimeFolderTriSurfaceFields(geomFolder, folders.time(), destFolder, "surface"))
+			
+			if(!pFlow::TSFtoVTK::convertTimeFolderTriSurfaceFields(
+				Control, destFolder, "surface", separateSurfaces))
 			{
 				fatalExit;
 				return 1;
 			}	
-		}*/
+		}
 
 		if(!noParticle)
 		{
diff --git a/utilities/pFlowToVTK/triSurfaceFieldToVTK.cpp b/utilities/pFlowToVTK/triSurfaceFieldToVTK.cpp
new file mode 100644
index 00000000..b7151db7
--- /dev/null
+++ b/utilities/pFlowToVTK/triSurfaceFieldToVTK.cpp
@@ -0,0 +1,349 @@
+#include "vocabs.hpp"
+#include "vtkFile.hpp"
+#include "triSurfaceFieldToVTK.hpp"
+
+bool pFlow::TSFtoVTK::convertTimeFolderTriSurfaceFields(
+    systemControl &control,
+    const fileSystem &destPath,
+    const word &bName,
+    bool separate)
+{
+
+    auto timeFolder = control.geometry().path();
+
+    // check if pointStructure exist in this folder
+    IOfileHeader triSurfaeHeader(
+        objectFile(
+            triSurfaceFile__,
+            timeFolder,
+            objectFile::READ_ALWAYS,
+            objectFile::WRITE_ALWAYS));
+
+    if (!triSurfaeHeader.headerOk(true))
+    {
+        WARNING << "Time folder " << timeFolder << " does not contain any triSurface data file."
+                << " Skipping this folder . . ." << END_WARNING;
+        return true;
+    }
+
+    auto triSurfaceObj = multiTriSurface(
+        objectFile(
+            triSurfaceFile__,
+            "",
+            objectFile::READ_ALWAYS,
+            objectFile::WRITE_ALWAYS),
+        &control.geometry());
+
+    if(separate)
+    {
+        return convertTimeFolderTriSurfaceFieldsSeparate(
+            triSurfaceObj,
+            destPath,
+            control.time().currentTime(),
+            bName);
+    }
+    else
+    {
+        return convertTimeFolderTriSurfaceFieldsSingle(
+            triSurfaceObj,
+            destPath,
+            control.time().currentTime(),
+            bName );
+    }
+}
+
+bool pFlow::TSFtoVTK::triSurfaceToVTK(
+    iOstream &os, 
+    const realx3 *points, 
+    const uint32x3 *vertices, 
+    const subSurface &subSurf)
+{
+    auto nP = subSurf.numPoints();
+	
+	os << "DATASET UNSTRUCTURED_GRID" << endl;
+	os << "POINTS " << nP << " float" << endl;
+
+	for ( auto i=subSurf.pointStart(); i<subSurf.pointEnd(); i++ )
+	{
+		os << points[i].x()  << 
+        " " << points[i].y() << 
+        " " << points[i].z() << endl;
+		if (!os) return false;
+	}
+
+	auto nTri = subSurf.size();
+	
+	os << "CELLS " << nTri << " " << 4*nTri << endl;
+
+	for(auto i=subSurf.start(); i<subSurf.end(); i++)
+	{
+		os<< 3 <<
+        " "<< vertices[i].x()-subSurf.pointStart() << 
+        " "<< vertices[i].y()-subSurf.pointStart() <<
+        " "<< vertices[i].z()-subSurf.pointStart()<<endl;
+		if (!os) return false;
+	}
+
+    os<<"CELL_TYPES "<< nTri<<'\n';
+
+	for(uint32 i=0; i<nTri; i++)
+	{
+		os<< 5 <<'\n';
+	}
+	
+	os << "CELL_DATA " << nTri << endl;
+
+	return true;
+}
+
+bool pFlow::TSFtoVTK::triSurfaceToVTK(
+    iOstream &os, 
+    const realx3 *points, 
+    const uint32x3 *vertices, 
+    uint32 numPoints, 
+    uint32 numTris)
+{
+
+	os << "DATASET UNSTRUCTURED_GRID" << endl;
+	os << "POINTS " << numPoints << " float" << endl;
+
+	for ( auto i=0; i<numPoints; i++ )
+	{
+		os << points[i].x()  << 
+        " " << points[i].y() << 
+        " " << points[i].z() << endl;
+		if (!os) return false;
+	}
+	
+	os << "CELLS " << numTris << " " << 4*numTris << endl;
+
+	for(auto i=0; i<numTris; i++)
+	{
+		os<< 3 <<
+        " "<< vertices[i].x()<< 
+        " "<< vertices[i].y()<<
+        " "<< vertices[i].z()<<endl;
+		if (!os) return false;
+	}
+
+    os<<"CELL_TYPES "<< numTris<<'\n';
+
+	for(uint32 i=0; i<numTris; i++)
+	{
+		os<< 5 <<'\n';
+	}
+	
+	os << "CELL_DATA " << numTris << endl;
+
+	return true;
+}
+
+bool pFlow::TSFtoVTK::convertTimeFolderTriSurfaceFieldsSingle
+(
+    multiTriSurface &surface, 
+    const fileSystem &destPath,
+    real time, 
+    const word &bName
+)
+{
+    vtkFile vtk(destPath, bName, time);
+
+    if (!vtk)
+        return false;
+    
+    auto hPoints = surface.points().hostView();
+    auto hVertices = surface.vertices().hostView();
+
+    realx3 const* pData = hPoints.data();
+    uint32x3 const* vData = hVertices.data();
+
+    REPORT(1) << "Wrting triSurface geometry to vtk file "<<
+    Green_Text(vtk.fileName()) << END_REPORT;
+    
+    if (! triSurfaceToVTK(
+        vtk(), 
+        pData, 
+        vData, 
+        surface.numPoints(), 
+        surface.size()))
+    {
+        fatalErrorInFunction << 
+        "error in writing triSurface data to vtk file " << 
+        vtk.fileName() << endl;
+        return false;
+    }
+
+    auto fileList = containingFiles(surface.path().dirPath());
+
+    for(const auto& file:fileList)
+    {
+        IOfileHeader fieldHeader(
+            objectFile(
+            file.fileName(),
+            file.dirPath(), 
+            objectFile::READ_ALWAYS,
+            objectFile::WRITE_ALWAYS) );
+
+        if( fieldHeader.headerOk(true) )
+        {            
+            convertRealx3TypetriSurfaceField(vtk(), fieldHeader, surface);
+        }
+    }
+
+    output<<endl;
+    return true;
+}
+
+bool pFlow::TSFtoVTK::convertTimeFolderTriSurfaceFieldsSeparate(
+    multiTriSurface &surface, 
+    const fileSystem &destPath, 
+    real time, 
+    const word &bName)
+{
+    
+    auto hPoints = surface.points().hostView();
+    auto hVertices = surface.vertices().hostView();
+
+    realx3 const* pData = hPoints.data();
+    uint32x3 const* vData = hVertices.data();
+
+    REPORT(1) << "Wrting triSurface geometry to vtk file . . ."<<
+    END_REPORT;
+
+    auto nSurf = surface.numSurfaces();
+    for(auto nS=0; nS<nSurf; nS++)
+    {
+        auto sName = surface.subSurfaceName(nS);    
+        vtkFile vtk(destPath, groupNames(bName,sName), time);
+        REPORT(2) << "Wrting sub-surface to "<<
+        Green_Text(vtk.fileName())<<END_REPORT;
+
+        if (!vtk)
+            return false;
+
+        if (! triSurfaceToVTK(
+            vtk(), 
+            pData, 
+            vData, 
+            surface.subSurfaces()[nS]) )
+        {
+            fatalErrorInFunction << 
+            "error in writing triSurface data to vtk file " << 
+            vtk.fileName() << endl;
+            return false;
+        }
+    } 
+
+    auto fileList = containingFiles(surface.path().dirPath());
+
+    for(const auto& file:fileList)
+    {
+        IOfileHeader fieldHeader(
+            objectFile(
+            file.fileName(),
+            file.dirPath(), 
+            objectFile::READ_ALWAYS,
+            objectFile::WRITE_ALWAYS) );
+
+        if( fieldHeader.headerOk(true) )
+        {
+            convertRealx3TypetriSurfaceFieldSeparate(
+                destPath,
+                fieldHeader,
+                surface,
+                bName,
+                time);
+        }
+
+    } 
+
+    output<<endl;
+    return true;
+}
+
+
+bool pFlow::TSFtoVTK::convertRealx3TypetriSurfaceField(
+	iOstream& os,
+	const IOfileHeader& header,
+	multiTriSurface& tSurface)
+{
+	word objectType = header.objectType();
+    
+	if(!checkTriFieldType<realx3>(objectType))return false;
+
+	auto field = realx3TriSurfaceField_H
+	(
+		header,
+		tSurface,
+		static_cast<real>(0)
+	);
+
+	const realx3* data = field.deviceViewAll().data();
+	
+	REPORT(1)<<"writing "<< greenColor <<header.objectName()<<
+    defaultColor<<" field to vtk."<<END_REPORT;
+
+    return pFlow::PFtoVTK::addRealx3PointField
+    (
+        os, 
+        header.objectName(),
+        data,
+        field.size()
+    );
+}
+
+
+bool pFlow::TSFtoVTK::convertRealx3TypetriSurfaceFieldSeparate
+(
+	const fileSystem& destPath,
+	const IOfileHeader& header,
+	multiTriSurface& tSurface,
+    const word& bName,
+    real time
+)
+{
+    word objectType = header.objectType();
+    
+	if(!checkTriFieldType<realx3>(objectType))return false;
+
+	auto field = realx3TriSurfaceField_H
+	(
+		header,
+		tSurface,
+		static_cast<real>(0)
+	);
+
+	const realx3* data = field.deviceViewAll().data();
+	
+	/*REPORT(1)<<"writing "<< greenColor <<header.objectName()<<
+    defaultColor<<" field to vtk."<<END_REPORT;*/
+
+    auto nSurf = tSurface.numSurfaces();
+
+    for(auto nS=0; nS<nSurf; nS++)
+    {
+        auto& subSurf = tSurface.subSurfaces()[nS];
+
+        auto sName = subSurf.name();    
+        vtkFile vtk(destPath, groupNames(bName,sName), time, true);
+        REPORT(2) << "Wrting sub-surface to "<<
+        Green_Text(vtk.fileName())<<END_REPORT;
+
+        pFlow::PFtoVTK::addRealx3PointField
+        (
+            vtk(), 
+            header.objectName(),
+            data+subSurf.start(),
+            subSurf.size()
+        );
+    }
+
+    return true;
+    /*return pFlow::PFtoVTK::addRealx3PointField
+    (
+        os, 
+        header.objectName(),
+        data,
+        field.size()
+    );*/
+}
\ No newline at end of file
diff --git a/utilities/pFlowToVTK/triSurfaceFieldToVTK.hpp b/utilities/pFlowToVTK/triSurfaceFieldToVTK.hpp
index d749a637..dc5a384b 100644
--- a/utilities/pFlowToVTK/triSurfaceFieldToVTK.hpp
+++ b/utilities/pFlowToVTK/triSurfaceFieldToVTK.hpp
@@ -24,19 +24,51 @@ Licence:
 
 #include <regex>
 
-#include "vtkFile.hpp"
+#include "pointFieldToVTK.hpp"
 #include "triSurface.hpp"
 #include "multiTriSurface.hpp"
 #include "triSurfaceFields.hpp"
-#include "IOobject.hpp"
+
 
 namespace pFlow::TSFtoVTK
 {
 
-bool regexCheck(word TYPENAME, word fieldType)
+bool convertTimeFolderTriSurfaceFields( 
+	systemControl& control,
+	const fileSystem& destPath,
+	const word& bName,
+	bool separate);
+
+
+bool triSurfaceToVTK(iOstream &os,
+					const realx3 *points,
+					const uint32x3 *vertices,
+					const subSurface &subSurf);
+
+bool triSurfaceToVTK(iOstream &os,
+					const realx3* points,
+					const uint32x3* vertices,
+					uint32 numPoints,
+					uint32 numTris);
+
+bool convertTimeFolderTriSurfaceFieldsSingle( 
+	multiTriSurface& surface,
+	const fileSystem& destPath,
+	real  time,
+	const word& bName);
+
+bool convertTimeFolderTriSurfaceFieldsSeparate( 
+	multiTriSurface& surface,
+	const fileSystem& destPath,
+	real  time,
+	const word& bName);
+
+inline
+bool regexCheck(const word& TYPENAME, const word& fieldType)
 {
 	std::regex match("triSurfaceField\\<([A-Za-z1-9_]*)\\,([A-Za-z1-9_]*)\\>");
-	std::smatch search1, search2;
+	std::smatch search1;
+	std::smatch search2;
 	if(!std::regex_match(fieldType, search1, match))return false;
 	if(!std::regex_match(TYPENAME, search2, match))return false;
 	if(search1.size()!=3)return false;
@@ -45,201 +77,27 @@ bool regexCheck(word TYPENAME, word fieldType)
 }
 
 template<typename Type>
-bool checkFieldType(word objectType)
+inline
+bool checkTriFieldType(word objectType)
 {
-	//if( pointField<VectorSingle,Type>::TYPENAME() == objectType )return true;
-	//if( pointField<VectorSingle,Type, HostSpace>::TYPENAME() == objectType ) return true;
-	//if( pointField<VectorDual, Type>::TYPENAME() == objectType )return true;
-	return regexCheck(triSurfaceField<VectorSingle,Type>::TYPENAME(), objectType);
-	
-}
-
-template<typename Type>
-bool triDataToVTK(iOstream& os, const Type& dataEntity)
-{
-	fatalErrorInFunction<<
-	"not implemented function!";
-	fatalExit;
-	return false;
-}
-
-template<>
-bool triDataToVTK(iOstream& os, const triSurface& surface )
-{
-	auto nP = surface.numPoints();
-	auto hPoints = surface.points().hostVector();
-
-	os << "DATASET POLYDATA" << endl;
-	os << "POINTS " << nP << " float" << endl;
-
-
-	for ( auto i=0; i<nP; i++ )
-	{
-		os << hPoints[i].x()  << " " << hPoints[i].y() << " " << hPoints[i].z() << endl;
-	}
-
-	auto nV = surface.numTriangles();
-	auto hVertices = surface.vertices().hostVector();
-
-	os << "POLYGONS " << nV << "  " << 4*nV << endl;
-
-	for(auto i=0; i<nV; i++)
-	{
-		os<< 3 <<" "<< hVertices[i].x() << " " << hVertices[i].y() <<" "<<hVertices[i].z()<<endl;
-	}
-
-	return true;
-}
-
-template<>
-bool triDataToVTK(iOstream& os, const multiTriSurface& surface )
-{
-	auto nP = surface.numPoints();
-	auto hPoints = surface.points().hostVector();
-
-	os << "DATASET UNSTRUCTURED_GRID" << endl;
-	os << "POINTS " << nP << " float" << endl;
-
-
-	for ( auto i=0; i<nP; i++ )
-	{
-		os << hPoints[i].x()  << " " << hPoints[i].y() << " " << hPoints[i].z() << endl;
-	}
-
-	auto nV = surface.numTriangles();
-	auto hVertices = surface.vertices().hostVector();
-
-	os<<"CELLS "<< nV<<' '<< 4*nV<<'\n';
-	//os << "POLYGONS " << nV << "  " << 4*nV << endl;
-
-	for(auto i=0; i<nV; i++)
-	{
-		os<< 3 <<" "<< hVertices[i].x() << " " << hVertices[i].y() <<" "<<hVertices[i].z()<<endl;
-	}
-
-	os<<"CELL_TYPES "<< nV<<'\n';
-
-	for(int32 i=0; i<nV; i++)
-	{
-		os<< 5 <<'\n';
-	}
-	
-	os << "CELL_DATA " << nV << endl;
-
-	return true;
-}
-
-bool addRealx3TriSurfaceField(
-	iOstream& 	os,
-	word 		fieldName,
-	int32 		size,
-	realx3* 	field )
-{
-	if(size==0) return true;
-
-
-	os << "FIELD FieldData 1\n"<<
-	fieldName << " 3 " << size << " float\n";
-	for(int32 i=0; i<size; ++i)
-	{
-			os<< field[i].x()<<' '<< field[i].y()<<' '<<field[i].z()<<'\n';
-	}
-
-	return true;
+	return regexCheck(triSurfaceField<Type>::TYPENAME(), objectType);
 }
 
 bool convertRealx3TypetriSurfaceField(
 	iOstream& os,
 	const IOfileHeader& header,
-	const multiTriSurface& tSurface)
-{
-	word objectType = header.objectType();
+	multiTriSurface& tSurface);
 
-	if(!checkFieldType<realx3>(objectType))return false;
-
-	auto objField = IOobject::make<realx3TriSurfaceField_H>
-	(
-		header,
-		tSurface,
-		static_cast<real>(0)
-	);
-
-	auto& Field = objField().getObject<realx3TriSurfaceField_H>();
-
-	realx3* data = Field.hostVectorAll().data();
-	
-	REPORT(2)<<"writing "<< greenColor <<header.objectName()<<defaultColor<<" field to vtk."<<endREPORT;
-
-	return addRealx3TriSurfaceField(
-		os,
-		header.objectName(),
-		tSurface.size(),
-		data );
-}
-
-bool convertTimeFolderTriSurfaceFields( 
-	fileSystem timeFolder,
-	real time,
-	fileSystem destPath,
-	word bName)
-{
-
-	// check if pointStructure exist in this folder 
-	IOfileHeader triSurfaeHeader(
-		objectFile(
-			triSurfaceFile__,
-			timeFolder,
-			objectFile::READ_ALWAYS,
-			objectFile::WRITE_ALWAYS)
-		);
-
-	if( !triSurfaeHeader.headerOk(true) )
-	{
-		output<<yellowText("Time folder "<< timeFolder <<
-		" does not contain any triSurface data file. Skipping this folder . . ."
-		)<<nl;
-		return true;
-	}
-
-	vtkFile vtk(destPath, bName, time);
-
-	if(!vtk) return false;
-
-	auto triSurfaceObjPtr = IOobject::make<multiTriSurface>(triSurfaeHeader);
-	auto& tSurface = triSurfaceObjPtr().getObject<multiTriSurface>();
-
-	// get a list of files in this timeFolder;
-	REPORT(1)<<"Wrting triSurface mesh/Geometry to vtk file."<<endREPORT;
-	if(!triDataToVTK(vtk(), tSurface))
-	{
-		fatalErrorInFunction<<
-		"error in writing triSurface data to vtk file "<< vtk.fileName()<<endl;
-		return false;
-	}
+bool convertRealx3TypetriSurfaceFieldSeparate(
+	const fileSystem& destPath,
+	const IOfileHeader& header,
+	multiTriSurface& tSurface,
+	const word& bName,
+	real time);
 
 
-	auto fileList = containingFiles(timeFolder);
 
 
-	for(auto& file:fileList)
-	{
-		IOfileHeader fieldHeader(
-			objectFile(
-			file.wordPath(),
-			"",
-			objectFile::READ_ALWAYS,
-			objectFile::WRITE_ALWAYS) );
-
-		if( fieldHeader.headerOk(true) )
-		{
-			//output<<"object file type is "<<fieldHeader.objectType()<<endl;
-			convertRealx3TypetriSurfaceField(vtk(), fieldHeader, tSurface);
-		}
-	}
-
-	return true;
-}
-
 }
 
 #endif