diff --git a/pylot/core/active/ActiveSeismoPick3D_GUI.py b/pylot/core/active/ActiveSeismoPick3D_GUI.py
index e39e4c8d..b91caada 100755
--- a/pylot/core/active/ActiveSeismoPick3D_GUI.py
+++ b/pylot/core/active/ActiveSeismoPick3D_GUI.py
@@ -12,6 +12,7 @@ from generate_survey_layout import *
 from generate_survey_layout_minimal import *
 from generate_seisarray_layout import *
 from picking_parameters_layout import *
+from vtk_tools_layout import *
 from pylot.core.active import activeSeismoPick, surveyUtils, fmtomoUtils, seismicArrayPreparation
 
 from matplotlib.backends.backend_qt4agg import FigureCanvasQTAgg as FigureCanvas
@@ -50,6 +51,7 @@ class gui_control(object):
         QtCore.QObject.connect(self.mainUI.picker, QtCore.SIGNAL("clicked()"), self.callPicker)
         QtCore.QObject.connect(self.mainUI.postprocessing, QtCore.SIGNAL("clicked()"), self.postprocessing)
         QtCore.QObject.connect(self.mainUI.fmtomo, QtCore.SIGNAL("clicked()"), self.startFMTOMO)
+        QtCore.QObject.connect(self.mainUI.vtk_tools, QtCore.SIGNAL("clicked()"), self.startVTKtools)
         QtCore.QObject.connect(self.mainUI.comboBox, QtCore.SIGNAL("activated(int)"), self.replotStat)
 
     def gen_seisarray(self):
@@ -73,7 +75,10 @@ class gui_control(object):
             srcfile = self.gen_new_seisarray.lineEdit_src.text()
             recfile = self.gen_new_seisarray.lineEdit_rec.text()
             ptsfile = self.gen_new_seisarray.lineEdit_pts.text()
-            self.seisarray = seismicArrayPreparation.SeisArray(recfile)
+            if self.gen_new_seisarray.radioButton_interpolatable.isChecked():
+                self.seisarray = seismicArrayPreparation.SeisArray(recfile, True)
+            elif self.gen_new_seisarray.radioButton_normal.isChecked():
+                self.seisarray = seismicArrayPreparation.SeisArray(recfile, False)
             if len(srcfile) > 0:
                 self.seisarray.addSourceLocations(srcfile)
             if len(ptsfile) > 0:
@@ -247,6 +252,9 @@ class gui_control(object):
         if not self.checkSurveyState():
             self.printDialogMessage('No Survey defined.')
             return
+        if not self.checkPickState():
+            self.printDialogMessage('Survey not picked.')
+            return
         fmtomo_parameters = QtGui.QDialog(self.mainwindow)
         ui = Ui_fmtomo_parameters()
         ui.setupUi(fmtomo_parameters)                
@@ -256,6 +264,15 @@ class gui_control(object):
         self.connectButtons_startFMTOMO()
         self.getFMTOMOparameters(ui, fmtomo_parameters)
 
+    def startVTKtools(self):
+        vtk_tools = QtGui.QDialog(self.mainwindow)
+        ui = Ui_vtk_tools()
+        ui.setupUi(vtk_tools)
+
+        self.vtk_tools_ui = ui
+        self.connectButtons_vtk_tools()
+        #self.getFMTOMOparameters(ui, fmtomo_parameters)
+
     def getFMTOMOparameters(self, ui, fmtomo_parameters):
         if fmtomo_parameters.exec_():
             fmtomo_dir = ui.fmtomo_dir.text()
@@ -291,6 +308,40 @@ class gui_control(object):
         QtCore.QObject.connect(self.fmtomo_parameters_ui.browse_customgrid, QtCore.SIGNAL("clicked()"), self.chooseCustomgrid)
         QtCore.QObject.connect(self.fmtomo_parameters_ui.browse_simuldir, QtCore.SIGNAL("clicked()"), self.chooseSimuldir)
 
+    def connectButtons_vtk_tools(self):
+        QtCore.QObject.connect(self.vtk_tools_ui.pushButton_vg, QtCore.SIGNAL("clicked()"), self.chooseVgrid)
+        QtCore.QObject.connect(self.vtk_tools_ui.pushButton_vgref, QtCore.SIGNAL("clicked()"), self.chooseVgridref)
+        QtCore.QObject.connect(self.vtk_tools_ui.pushButton_rays, QtCore.SIGNAL("clicked()"), self.chooseRaysIn)
+        QtCore.QObject.connect(self.vtk_tools_ui.pushButton_raysout, QtCore.SIGNAL("clicked()"), self.chooseRaysOutDir)
+        QtCore.QObject.connect(self.vtk_tools_ui.start_vg, QtCore.SIGNAL("clicked()"), self.startvgvtk)
+        QtCore.QObject.connect(self.vtk_tools_ui.start_rays, QtCore.SIGNAL("clicked()"), self.startraysvtk)
+
+    def chooseVgrid(self):
+        self.vtk_tools_ui.lineEdit_vg.setText(self.openFile())
+
+    def chooseVgridref(self):
+        self.vtk_tools_ui.lineEdit_vgref.setText(self.openFile())
+
+    def chooseRaysIn(self):
+        self.vtk_tools_ui.lineEdit_rays.setText(self.openFile())
+
+    def chooseRaysOutDir(self):
+        self.vtk_tools_ui.lineEdit_raysout.setText(self.browseDir())
+
+    def startvgvtk(self):
+        if self.vtk_tools_ui.radioButton_abs.isChecked():
+            fmtomoUtils.vgrids2VTK(inputfile = self.vtk_tools_ui.lineEdit_vg.text(),
+                                   outputfile = 'vgrids_rel.vtk',
+                                   absOrRel='abs')
+        elif self.vtk_tools_ui.radioButton_rel.isChecked():
+            fmtomoUtils.vgrids2VTK(inputfile = self.vtk_tools_ui.lineEdit_vg.text(),
+                                   outputfile = 'vgrids_rel.vtk',
+                                   absOrRel='rel',
+                                   inputfileref = self.vtk_tools_ui.lineEdit_vgref.text())
+
+    def startraysvtk(self):
+        fmtomoUtils.rays2VTK()
+
     def chooseFMTOMOdir(self):
         self.fmtomo_parameters_ui.fmtomo_dir.setText(self.browseDir())
 
diff --git a/pylot/core/active/asp3d_layout.py b/pylot/core/active/asp3d_layout.py
index a1830674..9b48dea7 100644
--- a/pylot/core/active/asp3d_layout.py
+++ b/pylot/core/active/asp3d_layout.py
@@ -2,7 +2,7 @@
 
 # Form implementation generated from reading ui file 'asp3d_layout.ui'
 #
-# Created: Tue Jun 28 14:40:06 2016
+# Created: Tue Jul  5 13:55:55 2016
 #      by: pyside-uic 0.2.15 running on PySide 1.2.2
 #
 # WARNING! All changes made in this file will be lost!
@@ -27,8 +27,8 @@ class Ui_MainWindow(object):
         MainWindow.setWindowIcon(icon)
         self.centralwidget = QtGui.QWidget(MainWindow)
         self.centralwidget.setObjectName("centralwidget")
-        self.horizontalLayout_4 = QtGui.QHBoxLayout(self.centralwidget)
-        self.horizontalLayout_4.setObjectName("horizontalLayout_4")
+        self.gridLayout = QtGui.QGridLayout(self.centralwidget)
+        self.gridLayout.setObjectName("gridLayout")
         self.formLayout = QtGui.QFormLayout()
         self.formLayout.setSizeConstraint(QtGui.QLayout.SetDefaultConstraint)
         self.formLayout.setFieldGrowthPolicy(QtGui.QFormLayout.AllNonFixedFieldsGrow)
@@ -237,6 +237,24 @@ class Ui_MainWindow(object):
         self.fmtomo = QtGui.QPushButton(self.centralwidget)
         self.fmtomo.setObjectName("fmtomo")
         self.verticalLayout_4.addWidget(self.fmtomo)
+        self.label_9 = QtGui.QLabel(self.centralwidget)
+        sizePolicy = QtGui.QSizePolicy(QtGui.QSizePolicy.Minimum, QtGui.QSizePolicy.Fixed)
+        sizePolicy.setHorizontalStretch(0)
+        sizePolicy.setVerticalStretch(0)
+        sizePolicy.setHeightForWidth(self.label_9.sizePolicy().hasHeightForWidth())
+        self.label_9.setSizePolicy(sizePolicy)
+        font = QtGui.QFont()
+        font.setFamily("Sans Serif")
+        font.setPointSize(10)
+        font.setWeight(75)
+        font.setBold(True)
+        self.label_9.setFont(font)
+        self.label_9.setAlignment(QtCore.Qt.AlignCenter)
+        self.label_9.setObjectName("label_9")
+        self.verticalLayout_4.addWidget(self.label_9)
+        self.vtk_tools = QtGui.QPushButton(self.centralwidget)
+        self.vtk_tools.setObjectName("vtk_tools")
+        self.verticalLayout_4.addWidget(self.vtk_tools)
         self.verticalLayout_3.addLayout(self.verticalLayout_4)
         self.verticalLayout_5.addLayout(self.verticalLayout_3)
         self.formLayout.setLayout(0, QtGui.QFormLayout.LabelRole, self.verticalLayout_5)
@@ -259,7 +277,7 @@ class Ui_MainWindow(object):
         self.horizontalLayout_br.setObjectName("horizontalLayout_br")
         self.verticalLayout_right.addLayout(self.horizontalLayout_br)
         self.formLayout.setLayout(0, QtGui.QFormLayout.FieldRole, self.verticalLayout_right)
-        self.horizontalLayout_4.addLayout(self.formLayout)
+        self.gridLayout.addLayout(self.formLayout, 0, 0, 1, 1)
         MainWindow.setCentralWidget(self.centralwidget)
         self.menubar = QtGui.QMenuBar(MainWindow)
         self.menubar.setGeometry(QtCore.QRect(0, 0, 905, 23))
@@ -304,4 +322,7 @@ class Ui_MainWindow(object):
         self.label_8.setText(QtGui.QApplication.translate("MainWindow", "Simulation", None, QtGui.QApplication.UnicodeUTF8))
         self.fmtomo.setToolTip(QtGui.QApplication.translate("MainWindow", "Set parameters and call Fast Marching Tomography algorithm.", None, QtGui.QApplication.UnicodeUTF8))
         self.fmtomo.setText(QtGui.QApplication.translate("MainWindow", "FMTOMO Simulation", None, QtGui.QApplication.UnicodeUTF8))
+        self.label_9.setText(QtGui.QApplication.translate("MainWindow", "Visualization", None, QtGui.QApplication.UnicodeUTF8))
+        self.vtk_tools.setToolTip(QtGui.QApplication.translate("MainWindow", "Set parameters and call Fast Marching Tomography algorithm.", None, QtGui.QApplication.UnicodeUTF8))
+        self.vtk_tools.setText(QtGui.QApplication.translate("MainWindow", "VTK tools", None, QtGui.QApplication.UnicodeUTF8))
 
diff --git a/pylot/core/active/fmtomo_parameters_layout.py b/pylot/core/active/fmtomo_parameters_layout.py
index 1c11112b..70c8a32a 100644
--- a/pylot/core/active/fmtomo_parameters_layout.py
+++ b/pylot/core/active/fmtomo_parameters_layout.py
@@ -2,7 +2,7 @@
 
 # Form implementation generated from reading ui file 'fmtomo_parameters_layout.ui'
 #
-# Created: Tue Jun 28 14:40:06 2016
+# Created: Tue Jul  5 13:55:55 2016
 #      by: pyside-uic 0.2.15 running on PySide 1.2.2
 #
 # WARNING! All changes made in this file will be lost!
diff --git a/pylot/core/active/generate_seisarray_layout.py b/pylot/core/active/generate_seisarray_layout.py
index 0d6d75e1..9bb3173f 100644
--- a/pylot/core/active/generate_seisarray_layout.py
+++ b/pylot/core/active/generate_seisarray_layout.py
@@ -2,7 +2,7 @@
 
 # Form implementation generated from reading ui file 'generate_seisarray_layout.ui'
 #
-# Created: Tue Jun 28 14:40:06 2016
+# Created: Tue Jul  5 13:55:55 2016
 #      by: pyside-uic 0.2.15 running on PySide 1.2.2
 #
 # WARNING! All changes made in this file will be lost!
@@ -12,7 +12,7 @@ from PySide import QtCore, QtGui
 class Ui_generate_seisarray(object):
     def setupUi(self, generate_seisarray):
         generate_seisarray.setObjectName("generate_seisarray")
-        generate_seisarray.resize(400, 221)
+        generate_seisarray.resize(403, 221)
         generate_seisarray.setMinimumSize(QtCore.QSize(400, 220))
         icon = QtGui.QIcon()
         icon.addPixmap(QtGui.QPixmap("../asp3d_icon.png"), QtGui.QIcon.Normal, QtGui.QIcon.Off)
@@ -23,14 +23,27 @@ class Ui_generate_seisarray(object):
         self.verticalLayout.setObjectName("verticalLayout")
         self.verticalLayout_4 = QtGui.QVBoxLayout()
         self.verticalLayout_4.setObjectName("verticalLayout_4")
+        self.horizontalLayout = QtGui.QHBoxLayout()
+        self.horizontalLayout.setObjectName("horizontalLayout")
         self.label_rec = QtGui.QLabel(generate_seisarray)
-        sizePolicy = QtGui.QSizePolicy(QtGui.QSizePolicy.Preferred, QtGui.QSizePolicy.Fixed)
+        sizePolicy = QtGui.QSizePolicy(QtGui.QSizePolicy.Maximum, QtGui.QSizePolicy.Fixed)
         sizePolicy.setHorizontalStretch(0)
         sizePolicy.setVerticalStretch(0)
         sizePolicy.setHeightForWidth(self.label_rec.sizePolicy().hasHeightForWidth())
         self.label_rec.setSizePolicy(sizePolicy)
+        self.label_rec.setToolTip("")
         self.label_rec.setObjectName("label_rec")
-        self.verticalLayout_4.addWidget(self.label_rec)
+        self.horizontalLayout.addWidget(self.label_rec)
+        spacerItem = QtGui.QSpacerItem(40, 20, QtGui.QSizePolicy.Expanding, QtGui.QSizePolicy.Minimum)
+        self.horizontalLayout.addItem(spacerItem)
+        self.radioButton_normal = QtGui.QRadioButton(generate_seisarray)
+        self.radioButton_normal.setChecked(True)
+        self.radioButton_normal.setObjectName("radioButton_normal")
+        self.horizontalLayout.addWidget(self.radioButton_normal)
+        self.radioButton_interpolatable = QtGui.QRadioButton(generate_seisarray)
+        self.radioButton_interpolatable.setObjectName("radioButton_interpolatable")
+        self.horizontalLayout.addWidget(self.radioButton_interpolatable)
+        self.verticalLayout_4.addLayout(self.horizontalLayout)
         self.horizontalLayout_4 = QtGui.QHBoxLayout()
         self.horizontalLayout_4.setObjectName("horizontalLayout_4")
         self.lineEdit_rec = QtGui.QLineEdit(generate_seisarray)
@@ -95,11 +108,27 @@ class Ui_generate_seisarray(object):
 
     def retranslateUi(self, generate_seisarray):
         generate_seisarray.setWindowTitle(QtGui.QApplication.translate("generate_seisarray", "Generate new Seismic Array", None, QtGui.QApplication.UnicodeUTF8))
-        self.label_rec.setToolTip(QtGui.QApplication.translate("generate_seisarray", "<!DOCTYPE HTML PUBLIC \"-//W3C//DTD HTML 4.0//EN\" \"http://www.w3.org/TR/REC-html40/strict.dtd\">\n"
+        self.label_rec.setText(QtGui.QApplication.translate("generate_seisarray", "Measured Receivers", None, QtGui.QApplication.UnicodeUTF8))
+        self.radioButton_normal.setToolTip(QtGui.QApplication.translate("generate_seisarray", "<!DOCTYPE HTML PUBLIC \"-//W3C//DTD HTML 4.0//EN\" \"http://www.w3.org/TR/REC-html40/strict.dtd\">\n"
 "<html><head><meta name=\"qrichtext\" content=\"1\" /><style type=\"text/css\">\n"
 "p, li { white-space: pre-wrap; }\n"
 "</style></head><body style=\" font-family:\'Sans\'; font-size:10pt; font-weight:400; font-style:normal;\">\n"
-"<p style=\" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;\">Load<span style=\" font-weight:600;\"> measured </span>receiver input file. The input file must be in the following format:</p>\n"
+"<p style=\" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;\">Load <span style=\" font-weight:600;\">normal </span>measured receiver input file. The input file must be in the following format:</p>\n"
+"<p style=\"-qt-paragraph-type:empty; margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;\"></p>\n"
+"<p style=\" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;\">Containing in each line, separated by spaces:</p>\n"
+"<p style=\"-qt-paragraph-type:empty; margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;\"></p>\n"
+"<p style=\" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;\">[trace ID (int)]  [X (float)]  [Y (float)]  [Z (float)]</p>\n"
+"<p style=\"-qt-paragraph-type:empty; margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;\"></p>\n"
+"<p style=\" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;\"><span style=\" font-weight:600;\">For example:</span></p>\n"
+"<p style=\" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;\">Geophone with the trace ID 50 and the coordinates (10.5 [m], 20.4 [m], 30.3 [m]).</p>\n"
+"<p style=\"-qt-paragraph-type:empty; margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;\"></p>\n"
+"<p style=\" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;\">50  10.5  20.4  30.3</p></body></html>", None, QtGui.QApplication.UnicodeUTF8))
+        self.radioButton_normal.setText(QtGui.QApplication.translate("generate_seisarray", "normal [?]", None, QtGui.QApplication.UnicodeUTF8))
+        self.radioButton_interpolatable.setToolTip(QtGui.QApplication.translate("generate_seisarray", "<!DOCTYPE HTML PUBLIC \"-//W3C//DTD HTML 4.0//EN\" \"http://www.w3.org/TR/REC-html40/strict.dtd\">\n"
+"<html><head><meta name=\"qrichtext\" content=\"1\" /><style type=\"text/css\">\n"
+"p, li { white-space: pre-wrap; }\n"
+"</style></head><body style=\" font-family:\'Sans\'; font-size:10pt; font-weight:400; font-style:normal;\">\n"
+"<p style=\" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;\">Load<span style=\" font-weight:600;\"> </span>measured receiver input file that can be <span style=\" font-weight:600;\">interpolated</span>. The input file must be in the following format:</p>\n"
 "<p style=\"-qt-paragraph-type:empty; margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;\"></p>\n"
 "<p style=\" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;\">Containing in each line, separated by spaces:</p>\n"
 "<p style=\"-qt-paragraph-type:empty; margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;\"></p>\n"
@@ -109,7 +138,7 @@ class Ui_generate_seisarray(object):
 "<p style=\" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;\">Third geophone on the second receiver line with the trace ID 50 and the coordinates (10.5 [m], 20.4 [m], 30.3 [m]).</p>\n"
 "<p style=\"-qt-paragraph-type:empty; margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;\"></p>\n"
 "<p style=\" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;\">50  2  3  10.5  20.4  30.3</p></body></html>", None, QtGui.QApplication.UnicodeUTF8))
-        self.label_rec.setText(QtGui.QApplication.translate("generate_seisarray", "Measured Receivers [?]", None, QtGui.QApplication.UnicodeUTF8))
+        self.radioButton_interpolatable.setText(QtGui.QApplication.translate("generate_seisarray", "interpolatable [?]", None, QtGui.QApplication.UnicodeUTF8))
         self.pushButton_rec.setText(QtGui.QApplication.translate("generate_seisarray", "Browse", None, QtGui.QApplication.UnicodeUTF8))
         self.label_src.setToolTip(QtGui.QApplication.translate("generate_seisarray", "<!DOCTYPE HTML PUBLIC \"-//W3C//DTD HTML 4.0//EN\" \"http://www.w3.org/TR/REC-html40/strict.dtd\">\n"
 "<html><head><meta name=\"qrichtext\" content=\"1\" /><style type=\"text/css\">\n"
diff --git a/pylot/core/active/generate_survey_layout.py b/pylot/core/active/generate_survey_layout.py
index ad197771..57cf02b0 100644
--- a/pylot/core/active/generate_survey_layout.py
+++ b/pylot/core/active/generate_survey_layout.py
@@ -2,7 +2,7 @@
 
 # Form implementation generated from reading ui file 'generate_survey_layout.ui'
 #
-# Created: Tue Jun 28 14:40:06 2016
+# Created: Tue Jul  5 13:55:56 2016
 #      by: pyside-uic 0.2.15 running on PySide 1.2.2
 #
 # WARNING! All changes made in this file will be lost!
diff --git a/pylot/core/active/generate_survey_layout_minimal.py b/pylot/core/active/generate_survey_layout_minimal.py
index c0af304b..59fb1923 100644
--- a/pylot/core/active/generate_survey_layout_minimal.py
+++ b/pylot/core/active/generate_survey_layout_minimal.py
@@ -2,7 +2,7 @@
 
 # Form implementation generated from reading ui file 'generate_survey_layout_minimal.ui'
 #
-# Created: Tue Jun 28 14:40:07 2016
+# Created: Tue Jul  5 13:55:56 2016
 #      by: pyside-uic 0.2.15 running on PySide 1.2.2
 #
 # WARNING! All changes made in this file will be lost!
diff --git a/pylot/core/active/picking_parameters_layout.py b/pylot/core/active/picking_parameters_layout.py
index d3208eab..af133884 100644
--- a/pylot/core/active/picking_parameters_layout.py
+++ b/pylot/core/active/picking_parameters_layout.py
@@ -2,7 +2,7 @@
 
 # Form implementation generated from reading ui file 'picking_parameters_layout.ui'
 #
-# Created: Tue Jun 28 14:40:07 2016
+# Created: Tue Jul  5 13:55:56 2016
 #      by: pyside-uic 0.2.15 running on PySide 1.2.2
 #
 # WARNING! All changes made in this file will be lost!
diff --git a/pylot/core/active/seismicArrayPreparation.py b/pylot/core/active/seismicArrayPreparation.py
index ba391bb0..abfda89f 100644
--- a/pylot/core/active/seismicArrayPreparation.py
+++ b/pylot/core/active/seismicArrayPreparation.py
@@ -17,18 +17,29 @@ class SeisArray(object):
     Note: Source and Receiver files for FMTOMO will be generated by the Survey object (because traveltimes will be added directly).
     '''
 
-    def __init__(self, recfile):
+    def __init__(self, recfile, interpolatable = False):
         self.recfile = recfile
-        self._receiverlines = {}
         self._receiverCoords = {}
         self._measuredReceivers = {}
         self._measuredTopo = {}
         self._sourceCoords = {}
-        self._geophoneNumbers = {}
         self._receiverlist = open(self.recfile, 'r').readlines()
-        self._generateReceiverlines()
-        self._setReceiverCoords()
+        if interpolatable == True:
+            self._init_interpolatable()
+        elif interpolatable == False:
+            self._init_normal()
+
+    def _init_normal(self):
+        self.interpolatable = False
+        self._setReceiverCoords_normal()
+
+    def _init_interpolatable(self):
+        self.interpolatable = True
+        self._receiverlines = {}
+        self._geophoneNumbers = {}
+        self._setReceiverCoords_interp()
         self._setGeophoneNumbers()
+        self._generateReceiverlines()
 
     def _generateReceiverlines(self):
         '''
@@ -42,9 +53,10 @@ class SeisArray(object):
                 self._receiverlines[lineID] = []
             self._receiverlines[lineID].append(traceID)
 
-    def _setReceiverCoords(self):
+    def _setReceiverCoords_interp(self):
         '''
         Fills the three x, y, z dictionaries with measured coordinates
+        in case of interpolatable measured input data.
         '''
         for line in self._getReceiverlist():
             traceID = int(line.split()[0])
@@ -54,6 +66,18 @@ class SeisArray(object):
             self._receiverCoords[traceID] = (x, y, z)
             self._measuredReceivers[traceID] = (x, y, z)
 
+    def _setReceiverCoords_normal(self):
+        '''
+        Fills the three x, y, z dictionaries with measured coordinates
+        '''
+        for line in self._getReceiverlist():
+            traceID = int(line.split()[0])
+            x = float(line.split()[1])
+            y = float(line.split()[2])
+            z = float(line.split()[3])
+            self._receiverCoords[traceID] = (x, y, z)
+            self._measuredReceivers[traceID] = (x, y, z)
+
     def _setGeophoneNumbers(self):
         for line in self._getReceiverlist():
             traceID = int(line.split()[0])
@@ -159,10 +183,17 @@ class SeisArray(object):
             self._getReceiverValue(traceID1, coordinate) - self._getReceiverValue(traceID2, coordinate)) / num_spaces
         return mean_distance
 
+    def checkInterpolatable(self):
+        if self.interpolatable == False:
+            print('Not interpolatable.')
+        return self.interpolatable
+
     def interpolateValues(self, coordinate):
         '''
         Interpolates and sets all values (linear) for coordinate = 'X', 'Y' or 'Z'
         '''
+        if not self.checkInterpolatable():
+            return
         for lineID in self._getReceiverlines().keys():
             number_measured = len(self._getReceiverlines()[lineID])
             for index, traceID1 in enumerate(self._getReceiverlines()[lineID]):
@@ -314,6 +345,8 @@ class SeisArray(object):
             self.interpolateValues(coordinate)
 
     def interpolateAll(self):
+        if not self.checkInterpolatable():
+            return
         self._interpolateXY4rec()
         self.interpZcoords4rec()
         print('Interpolated receiver locations.')
@@ -811,7 +844,7 @@ class SeisArray(object):
         ax.set_xlabel('X [m]')
         ax.set_ylabel('Y [m]')
         ax.set_aspect('equal')
-        ax.legend()
+        ax.legend(prop={'size':7})
         if annotations == True:
             for traceID in self.getReceiverCoordinates().keys():
                 ax.annotate((' ' + str(traceID)), xy=(self._getXreceiver(traceID), self._getYreceiver(traceID)),
diff --git a/pylot/core/active/vtk_tools_layout.py b/pylot/core/active/vtk_tools_layout.py
new file mode 100644
index 00000000..5fd15149
--- /dev/null
+++ b/pylot/core/active/vtk_tools_layout.py
@@ -0,0 +1,188 @@
+# -*- coding: utf-8 -*-
+
+# Form implementation generated from reading ui file 'vtk_tools_layout.ui'
+#
+# Created: Tue Jul  5 13:55:56 2016
+#      by: pyside-uic 0.2.15 running on PySide 1.2.2
+#
+# WARNING! All changes made in this file will be lost!
+
+from PySide import QtCore, QtGui
+
+class Ui_vtk_tools(object):
+    def setupUi(self, vtk_tools):
+        vtk_tools.setObjectName("vtk_tools")
+        vtk_tools.resize(406, 407)
+        self.verticalLayout_8 = QtGui.QVBoxLayout(vtk_tools)
+        self.verticalLayout_8.setObjectName("verticalLayout_8")
+        self.verticalLayout = QtGui.QVBoxLayout()
+        self.verticalLayout.setObjectName("verticalLayout")
+        self.verticalLayout_4 = QtGui.QVBoxLayout()
+        self.verticalLayout_4.setObjectName("verticalLayout_4")
+        self.horizontalLayout = QtGui.QHBoxLayout()
+        self.horizontalLayout.setObjectName("horizontalLayout")
+        self.label_rec = QtGui.QLabel(vtk_tools)
+        sizePolicy = QtGui.QSizePolicy(QtGui.QSizePolicy.Maximum, QtGui.QSizePolicy.Fixed)
+        sizePolicy.setHorizontalStretch(0)
+        sizePolicy.setVerticalStretch(0)
+        sizePolicy.setHeightForWidth(self.label_rec.sizePolicy().hasHeightForWidth())
+        self.label_rec.setSizePolicy(sizePolicy)
+        self.label_rec.setToolTip("")
+        self.label_rec.setObjectName("label_rec")
+        self.horizontalLayout.addWidget(self.label_rec)
+        spacerItem = QtGui.QSpacerItem(40, 20, QtGui.QSizePolicy.Expanding, QtGui.QSizePolicy.Minimum)
+        self.horizontalLayout.addItem(spacerItem)
+        self.radioButton_abs = QtGui.QRadioButton(vtk_tools)
+        self.radioButton_abs.setChecked(True)
+        self.radioButton_abs.setObjectName("radioButton_abs")
+        self.horizontalLayout.addWidget(self.radioButton_abs)
+        self.radioButton_rel = QtGui.QRadioButton(vtk_tools)
+        self.radioButton_rel.setObjectName("radioButton_rel")
+        self.horizontalLayout.addWidget(self.radioButton_rel)
+        self.verticalLayout_4.addLayout(self.horizontalLayout)
+        self.verticalLayout_6 = QtGui.QVBoxLayout()
+        self.verticalLayout_6.setObjectName("verticalLayout_6")
+        self.label_3 = QtGui.QLabel(vtk_tools)
+        self.label_3.setObjectName("label_3")
+        self.verticalLayout_6.addWidget(self.label_3)
+        self.horizontalLayout_2 = QtGui.QHBoxLayout()
+        self.horizontalLayout_2.setObjectName("horizontalLayout_2")
+        self.lineEdit_vg = QtGui.QLineEdit(vtk_tools)
+        self.lineEdit_vg.setObjectName("lineEdit_vg")
+        self.horizontalLayout_2.addWidget(self.lineEdit_vg)
+        self.pushButton_vg = QtGui.QPushButton(vtk_tools)
+        self.pushButton_vg.setObjectName("pushButton_vg")
+        self.horizontalLayout_2.addWidget(self.pushButton_vg)
+        self.verticalLayout_6.addLayout(self.horizontalLayout_2)
+        self.verticalLayout_4.addLayout(self.verticalLayout_6)
+        self.verticalLayout_7 = QtGui.QVBoxLayout()
+        self.verticalLayout_7.setObjectName("verticalLayout_7")
+        self.label_4 = QtGui.QLabel(vtk_tools)
+        self.label_4.setObjectName("label_4")
+        self.verticalLayout_7.addWidget(self.label_4)
+        self.horizontalLayout_4 = QtGui.QHBoxLayout()
+        self.horizontalLayout_4.setObjectName("horizontalLayout_4")
+        self.lineEdit_vgref = QtGui.QLineEdit(vtk_tools)
+        self.lineEdit_vgref.setEnabled(False)
+        self.lineEdit_vgref.setObjectName("lineEdit_vgref")
+        self.horizontalLayout_4.addWidget(self.lineEdit_vgref)
+        self.pushButton_vgref = QtGui.QPushButton(vtk_tools)
+        self.pushButton_vgref.setEnabled(False)
+        self.pushButton_vgref.setObjectName("pushButton_vgref")
+        self.horizontalLayout_4.addWidget(self.pushButton_vgref)
+        self.verticalLayout_7.addLayout(self.horizontalLayout_4)
+        self.start_vg = QtGui.QPushButton(vtk_tools)
+        self.start_vg.setEnabled(False)
+        self.start_vg.setObjectName("start_vg")
+        self.verticalLayout_7.addWidget(self.start_vg)
+        self.verticalLayout_4.addLayout(self.verticalLayout_7)
+        self.verticalLayout.addLayout(self.verticalLayout_4)
+        self.verticalLayout_2 = QtGui.QVBoxLayout()
+        self.verticalLayout_2.setObjectName("verticalLayout_2")
+        self.line = QtGui.QFrame(vtk_tools)
+        self.line.setFrameShape(QtGui.QFrame.HLine)
+        self.line.setFrameShadow(QtGui.QFrame.Sunken)
+        self.line.setObjectName("line")
+        self.verticalLayout_2.addWidget(self.line)
+        self.label_src = QtGui.QLabel(vtk_tools)
+        sizePolicy = QtGui.QSizePolicy(QtGui.QSizePolicy.Preferred, QtGui.QSizePolicy.Fixed)
+        sizePolicy.setHorizontalStretch(0)
+        sizePolicy.setVerticalStretch(0)
+        sizePolicy.setHeightForWidth(self.label_src.sizePolicy().hasHeightForWidth())
+        self.label_src.setSizePolicy(sizePolicy)
+        self.label_src.setObjectName("label_src")
+        self.verticalLayout_2.addWidget(self.label_src)
+        self.verticalLayout_3 = QtGui.QVBoxLayout()
+        self.verticalLayout_3.setObjectName("verticalLayout_3")
+        self.label = QtGui.QLabel(vtk_tools)
+        self.label.setObjectName("label")
+        self.verticalLayout_3.addWidget(self.label)
+        self.horizontalLayout_6 = QtGui.QHBoxLayout()
+        self.horizontalLayout_6.setObjectName("horizontalLayout_6")
+        self.lineEdit_rays = QtGui.QLineEdit(vtk_tools)
+        self.lineEdit_rays.setObjectName("lineEdit_rays")
+        self.horizontalLayout_6.addWidget(self.lineEdit_rays)
+        self.pushButton_rays = QtGui.QPushButton(vtk_tools)
+        self.pushButton_rays.setObjectName("pushButton_rays")
+        self.horizontalLayout_6.addWidget(self.pushButton_rays)
+        self.verticalLayout_3.addLayout(self.horizontalLayout_6)
+        self.verticalLayout_2.addLayout(self.verticalLayout_3)
+        self.verticalLayout_5 = QtGui.QVBoxLayout()
+        self.verticalLayout_5.setObjectName("verticalLayout_5")
+        self.label_2 = QtGui.QLabel(vtk_tools)
+        self.label_2.setObjectName("label_2")
+        self.verticalLayout_5.addWidget(self.label_2)
+        self.horizontalLayout_5 = QtGui.QHBoxLayout()
+        self.horizontalLayout_5.setObjectName("horizontalLayout_5")
+        self.lineEdit_raysout = QtGui.QLineEdit(vtk_tools)
+        self.lineEdit_raysout.setObjectName("lineEdit_raysout")
+        self.horizontalLayout_5.addWidget(self.lineEdit_raysout)
+        self.pushButton_raysout = QtGui.QPushButton(vtk_tools)
+        self.pushButton_raysout.setObjectName("pushButton_raysout")
+        self.horizontalLayout_5.addWidget(self.pushButton_raysout)
+        self.verticalLayout_5.addLayout(self.horizontalLayout_5)
+        self.start_rays = QtGui.QPushButton(vtk_tools)
+        self.start_rays.setEnabled(False)
+        self.start_rays.setObjectName("start_rays")
+        self.verticalLayout_5.addWidget(self.start_rays)
+        self.verticalLayout_2.addLayout(self.verticalLayout_5)
+        self.verticalLayout.addLayout(self.verticalLayout_2)
+        self.verticalLayout_8.addLayout(self.verticalLayout)
+        self.buttonBox = QtGui.QDialogButtonBox(vtk_tools)
+        self.buttonBox.setOrientation(QtCore.Qt.Horizontal)
+        self.buttonBox.setStandardButtons(QtGui.QDialogButtonBox.Cancel|QtGui.QDialogButtonBox.Ok)
+        self.buttonBox.setObjectName("buttonBox")
+        self.verticalLayout_8.addWidget(self.buttonBox)
+
+        self.retranslateUi(vtk_tools)
+        QtCore.QObject.connect(self.buttonBox, QtCore.SIGNAL("accepted()"), vtk_tools.accept)
+        QtCore.QObject.connect(self.buttonBox, QtCore.SIGNAL("rejected()"), vtk_tools.reject)
+        QtCore.QMetaObject.connectSlotsByName(vtk_tools)
+
+    def retranslateUi(self, vtk_tools):
+        vtk_tools.setWindowTitle(QtGui.QApplication.translate("vtk_tools", "VTK tools", None, QtGui.QApplication.UnicodeUTF8))
+        self.label_rec.setText(QtGui.QApplication.translate("vtk_tools", "Velocity grid to VTK", None, QtGui.QApplication.UnicodeUTF8))
+        self.radioButton_abs.setToolTip(QtGui.QApplication.translate("vtk_tools", "<!DOCTYPE HTML PUBLIC \"-//W3C//DTD HTML 4.0//EN\" \"http://www.w3.org/TR/REC-html40/strict.dtd\">\n"
+"<html><head><meta name=\"qrichtext\" content=\"1\" /><style type=\"text/css\">\n"
+"p, li { white-space: pre-wrap; }\n"
+"</style></head><body style=\" font-family:\'Sans\'; font-size:10pt; font-weight:400; font-style:normal;\">\n"
+"<p style=\" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;\">Load <span style=\" font-weight:600;\">normal </span>measured receiver input file. The input file must be in the following format:</p>\n"
+"<p style=\"-qt-paragraph-type:empty; margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;\"></p>\n"
+"<p style=\" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;\">Containing in each line, separated by spaces:</p>\n"
+"<p style=\"-qt-paragraph-type:empty; margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;\"></p>\n"
+"<p style=\" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;\">[trace ID (int)]  [X (float)]  [Y (float)]  [Z (float)]</p>\n"
+"<p style=\"-qt-paragraph-type:empty; margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;\"></p>\n"
+"<p style=\" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;\"><span style=\" font-weight:600;\">For example:</span></p>\n"
+"<p style=\" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;\">Geophone with the trace ID 50 and the coordinates (10.5 [m], 20.4 [m], 30.3 [m]).</p>\n"
+"<p style=\"-qt-paragraph-type:empty; margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;\"></p>\n"
+"<p style=\" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;\">50  10.5  20.4  30.3</p></body></html>", None, QtGui.QApplication.UnicodeUTF8))
+        self.radioButton_abs.setText(QtGui.QApplication.translate("vtk_tools", "absolute [?]", None, QtGui.QApplication.UnicodeUTF8))
+        self.radioButton_rel.setToolTip(QtGui.QApplication.translate("vtk_tools", "<!DOCTYPE HTML PUBLIC \"-//W3C//DTD HTML 4.0//EN\" \"http://www.w3.org/TR/REC-html40/strict.dtd\">\n"
+"<html><head><meta name=\"qrichtext\" content=\"1\" /><style type=\"text/css\">\n"
+"p, li { white-space: pre-wrap; }\n"
+"</style></head><body style=\" font-family:\'Sans\'; font-size:10pt; font-weight:400; font-style:normal;\">\n"
+"<p style=\" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;\">Load<span style=\" font-weight:600;\"> </span>measured receiver input file that can be <span style=\" font-weight:600;\">interpolated</span>. The input file must be in the following format:</p>\n"
+"<p style=\"-qt-paragraph-type:empty; margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;\"></p>\n"
+"<p style=\" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;\">Containing in each line, separated by spaces:</p>\n"
+"<p style=\"-qt-paragraph-type:empty; margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;\"></p>\n"
+"<p style=\" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;\">[trace ID (int)] [receiver line ID (int)] [number of the geophone on receiver line (int)]  [X (float)]  [Y (float)]  [Z (float)]</p>\n"
+"<p style=\"-qt-paragraph-type:empty; margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;\"></p>\n"
+"<p style=\" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;\"><span style=\" font-weight:600;\">For example:</span></p>\n"
+"<p style=\" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;\">Third geophone on the second receiver line with the trace ID 50 and the coordinates (10.5 [m], 20.4 [m], 30.3 [m]).</p>\n"
+"<p style=\"-qt-paragraph-type:empty; margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;\"></p>\n"
+"<p style=\" margin-top:0px; margin-bottom:0px; margin-left:0px; margin-right:0px; -qt-block-indent:0; text-indent:0px;\">50  2  3  10.5  20.4  30.3</p></body></html>", None, QtGui.QApplication.UnicodeUTF8))
+        self.radioButton_rel.setText(QtGui.QApplication.translate("vtk_tools", "relative [?]", None, QtGui.QApplication.UnicodeUTF8))
+        self.label_3.setText(QtGui.QApplication.translate("vtk_tools", "Browse for velocity grid file (\'vgrids.in\'):", None, QtGui.QApplication.UnicodeUTF8))
+        self.pushButton_vg.setText(QtGui.QApplication.translate("vtk_tools", "Browse", None, QtGui.QApplication.UnicodeUTF8))
+        self.label_4.setText(QtGui.QApplication.translate("vtk_tools", "Browse for reference velocity grid file (\'vgridsref.in\'):", None, QtGui.QApplication.UnicodeUTF8))
+        self.pushButton_vgref.setText(QtGui.QApplication.translate("vtk_tools", "Browse", None, QtGui.QApplication.UnicodeUTF8))
+        self.start_vg.setText(QtGui.QApplication.translate("vtk_tools", "Start", None, QtGui.QApplication.UnicodeUTF8))
+        self.label_src.setToolTip(QtGui.QApplication.translate("vtk_tools", "Create VTK files from the FMTOMO output file \'rays.dat\'.\n"
+"This will generate one file of ray paths for each individual source.", None, QtGui.QApplication.UnicodeUTF8))
+        self.label_src.setText(QtGui.QApplication.translate("vtk_tools", "Rays to VTK [?]", None, QtGui.QApplication.UnicodeUTF8))
+        self.label.setText(QtGui.QApplication.translate("vtk_tools", "Browse for input file (\'rays.dat\'):", None, QtGui.QApplication.UnicodeUTF8))
+        self.pushButton_rays.setText(QtGui.QApplication.translate("vtk_tools", "Browse", None, QtGui.QApplication.UnicodeUTF8))
+        self.label_2.setText(QtGui.QApplication.translate("vtk_tools", "Specify output directory:", None, QtGui.QApplication.UnicodeUTF8))
+        self.pushButton_raysout.setText(QtGui.QApplication.translate("vtk_tools", "Browse", None, QtGui.QApplication.UnicodeUTF8))
+        self.start_rays.setText(QtGui.QApplication.translate("vtk_tools", "Start", None, QtGui.QApplication.UnicodeUTF8))
+