3D Slicer

https://slicer.readthedocs.io/en/latest/
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### Launch Slicer using the start command

Source: https://slicer.readthedocs.io/en/latest/developer_guide/script_repository/gui.html

On Windows, the installer registers the Slicer application, allowing the 'start' command to launch the most recently installed Slicer and load an image.

```bash
start Slicer c:\some\folder\MRHead.nrrd
```

--------------------------------

### Add additional module paths at startup

Source: https://slicer.readthedocs.io/en/latest/user_guide/settings.html

Command-line example to start Slicer with additional module paths, loading CLIs from the specified directory. This is a temporary setting not saved in the application settings.

```bash
Slicer.exe --additional-module-paths C:\path\to\lib\Slicer-X.Y\cli-modules
```

--------------------------------

### Example configuration: sw_vers, qmake, cmake, system_profiler

Source: https://slicer.readthedocs.io/en/latest/developer_guide/build_instructions/macos.html

Shows the environment used for the arm64 build: macOS 15.7.3, Qt 6.10.1, CMake 3.31.5, and Apple M3 Pro hardware. Useful to compare with your own setup.

```bash
frolick@IsabelMacBook % sw_vers
ProductName:		macOS
ProductVersion:		15.7.3
BuildVersion:		24G419

frolick@IsabelMacBook % qmake --version
QMake version 3.1
Using Qt version 6.10.1 in /opt/homebrew/lib

frolick@IsabelMacBook % cmake --version
cmake version 3.31.5

CMake suite maintained and supported by Kitware (kitware.com/cmake).

frolick@IsabelMacBook % system_profiler SPHardwareDataType

Hardware:
    Hardware Overview:
      Model Name: MacBook Pro
      Model Identifier: Mac15,6
      Chip: Apple M3 Pro
      Total Number of Cores: 11 (5 performance and 6 efficiency)
      Memory: 36 GB

```

--------------------------------

### Install extension from server using slicer.app.installExtensionFromServer()

Source: https://slicer.readthedocs.io/en/latest/developer_guide/script_repository/gui.html

Downloads and installs an extension by name. Set `em.interactive = False` to prevent popups. Raises ValueError if installation fails.

```Python
extensionName = 'SlicerIGT'
em = slicer.app.extensionsManagerModel()
em.interactive = False  # prevent display of popups
restart = True
if not em.installExtensionFromServer(extensionName, restart):
  raise ValueError(f"Failed to install {extensionName} extension")
```

--------------------------------

### Install Qt6 via Homebrew and configure shell

Source: https://slicer.readthedocs.io/en/latest/developer_guide/build_instructions/macos.html

Installs Qt6 using Homebrew, adds Qt6 to the shell environment, reloads the shell, and verifies the installation. Requires Homebrew to be installed.

```bash
brew install qt@6

#Add Qt6 to shell environment
echo 'export PATH="/opt/homebrew/opt/qt@6/bin:$PATH"' >> ~/.zshrc
echo 'export CMAKE_PREFIX_PATH="/opt/homebrew/opt/qt@6:$CMAKE_PREFIX_PATH"' >> ~/.zshrc

#Reload shell
source ~/.zshrc

#Verify Qt6 installation
qmake --version

```

--------------------------------

### Build and install FFmpeg on Linux

Source: https://slicer.readthedocs.io/en/latest/user_guide/modules/screencapture.html

Run these commands in the terminal to clone, configure, and install FFmpeg with libx264 support. After installation, select ${HOME}/bin/ffmpeg in the Advanced section.

```bash
git clone https://git.ffmpeg.org/ffmpeg.git ffmpeg
cd ffmpeg
sudo apt-get install libx264-dev
./configure --enable-gpl --enable-libx264 --prefix=${HOME}
make install
```

--------------------------------

### Install Homebrew

Source: https://slicer.readthedocs.io/en/latest/developer_guide/build_instructions/macos.html

Run this command to install Homebrew on macOS.

```bash
$ /bin/bash -c "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/HEAD/install.sh)"
```

--------------------------------

### Install Python package with pip_install and progress dialog

Source: https://slicer.readthedocs.io/en/latest/developer_guide/script_repository/gui.html

Alternative to `pip_ensure` for direct installation with visual feedback. Shows a confirmation dialog and then installs with a progress dialog by default.

```Python
try:
  import flywheel
except ModuleNotFoundError:
  if slicer.util.confirmOkCancelDisplay("This module requires 'flywheel-sdk' Python package. Click OK to install it now."):
    slicer.packaging.pip_install("flywheel-sdk", requester="MyModule")
    import flywheel
```

--------------------------------

### Set up development environment

Source: https://slicer.readthedocs.io/en/latest/developer_guide/build_instructions/linux.html

Runs the setup script to prepare the development environment after cloning.

```bash
cd Slicer
./Utilities/SetupForDevelopment.sh
cd ..
```

--------------------------------

### Check pip install in progress and install scipy

Source: https://slicer.readthedocs.io/en/latest/developer_guide/slicer.html

Use slicer.packaging.isPipInstallInProgress() to check if a non-blocking pip install is in progress before starting an operation that might conflict. If in progress, show a warning; otherwise, install scipy non-blocking.

```python
if slicer.packaging.isPipInstallInProgress():
    slicer.util.warningDisplay(
        "Package installation is in progress. Please wait."
    )
else:
    slicer.packaging.pip_install("scipy", blocking=False)
```

--------------------------------

### Check if pip installation is in progress

Source: https://slicer.readthedocs.io/en/latest/developer_guide/script_repository.html

Before starting an operation that might conflict with an ongoing pip installation, check the in-progress flag with slicer.packaging.isPipInstallInProgress(). If true, display a warning; otherwise, proceed with installation.

```python
import slicer.packaging

if slicer.packaging.isPipInstallInProgress():
    slicer.util.warningDisplay("Package installation is in progress. Please wait.")
else:
    slicer.packaging.pip_install("scipy", blocking=False, requester="MyExtension")
```

--------------------------------

### Setup development environment

Source: https://slicer.readthedocs.io/en/latest/developer_guide/build_instructions/macos.html

Changes to the Slicer directory and runs the setup script to configure the development environment.

```bash
cd Slicer
./Utilities/SetupForDevelopment.sh
```

--------------------------------

### Start Slicer without CLI modules

Source: https://slicer.readthedocs.io/en/latest/user_guide/settings.html

Command-line example to start Slicer without loading any CLI modules. This is a temporary setting not saved in the application settings.

```bash
Slicer.exe --disable-cli-modules
```

--------------------------------

### Get a notification if a markup control point position is modified

Source: https://slicer.readthedocs.io/en/latest/developer_guide/script_repository/markups.html

Defines observer callbacks for point modification, start interaction, and end interaction events. The onMarkupChanged callback logs whether a point is previewed or moved, including the slice view. The example creates a fiducial node, adds a control point, and attaches observers to the PointModifiedEvent, PointStartInteractionEvent, and PointEndInteractionEvent.

```Python
def onMarkupChanged(caller,event):
  markupsNode = caller
  sliceView = markupsNode.GetAttribute(slicer.vtkMRMLMarkupsDisplayNode.GetMovingInSliceViewAttributeName())
  movingMarkupIndex = markupsNode.GetDisplayNode().GetActiveControlPoint()
  if movingMarkupIndex >= 0:
    pos = [0,0,0]
    markupsNode.GetNthControlPointPosition(movingMarkupIndex, pos)
    isPreview = markupsNode.GetNthControlPointPositionStatus(movingMarkupIndex) == slicer.vtkMRMLMarkupsNode.PositionPreview
    if isPreview:
      logging.info("Point {0} is previewed at {1} in slice view {2}".format(movingMarkupIndex, pos, sliceView))
    else:
      logging.info("Point {0} was moved {1} in slice view {2}".format(movingMarkupIndex, pos, sliceView))
  else:
    logging.info("Points modified: slice view = {0}".format(sliceView))

def onMarkupStartInteraction(caller, event):
  markupsNode = caller
  sliceView = markupsNode.GetAttribute(slicer.vtkMRMLMarkupsDisplayNode.GetMovingInSliceViewAttributeName())
  movingMarkupIndex = markupsNode.GetDisplayNode().GetActiveControlPoint()
  logging.info("Start interaction: point ID = {0}, slice view = {1}".format(movingMarkupIndex, sliceView))

def onMarkupEndInteraction(caller, event):
  markupsNode = caller
  sliceView = markupsNode.GetAttribute(slicer.vtkMRMLMarkupsDisplayNode.GetMovingInSliceViewAttributeName())
  movingMarkupIndex = markupsNode.GetDisplayNode().GetActiveControlPoint()
  logging.info("End interaction: point ID = {0}, slice view = {1}".format(movingMarkupIndex, sliceView))

pointListNode = slicer.mrmlScene.AddNewNodeByClass("vtkMRMLMarkupsFiducialNode")
pointListNode.AddControlPoint([0,0,0])
pointListNode.AddObserver(slicer.vtkMRMLMarkupsNode.PointModifiedEvent, onMarkupChanged)
pointListNode.AddObserver(slicer.vtkMRMLMarkupsNode.PointStartInteractionEvent, onMarkupStartInteraction)
pointListNode.AddObserver(slicer.vtkMRMLMarkupsNode.PointEndInteractionEvent, onMarkupEndInteraction)
```

--------------------------------

### Configure CMake with Qt5_DIR for Slicer build

Source: https://slicer.readthedocs.io/en/latest/developer_guide/build_instructions/linux.html

Sets the CMake variable Qt5_DIR to the Qt5 installation path ending with 5.15.2/gcc_64/lib/cmake/Qt5. Example assumes Qt is installed in /opt/qt.

```bash
cmake -DCMAKE_BUILD_TYPE:STRING=Release -DQt5_DIR:PATH=/opt/qt/5.15.2/gcc_64/lib/cmake/Qt5 ../Slicer
```

--------------------------------

### Download and make Qt online installer executable

Source: https://slicer.readthedocs.io/en/latest/developer_guide/build_instructions/linux.html

Downloads the Qt Linux online installer and makes it executable. Requires an account at qt.io.

```bash
curl -LO https://download.qt.io/official_releases/online_installers/qt-online-installer-linux-x64-online.run
chmod +x qt-online-installer-linux-x64-online.run
```

--------------------------------

### addParameterEditWidgetConnections example: SurfaceToolboxWidget

Source: https://slicer.readthedocs.io/en/latest/developer_guide/slicer.html

Shows how to connect parameter edit widgets to update the parameter node from GUI in a scripted module widget. The example includes setup, updateGUIFromParameterNode, and updateParameterNodeFromGUI methods.

```python
class SurfaceToolboxWidget(ScriptedLoadableModuleWidget, VTKObservationMixin):
  ...
  def setup(self):
    ...
    self.parameterEditWidgets = [
      (self.ui.inputModelSelector, "inputModel"),
      (self.ui.outputModelSelector, "outputModel"),
      (self.ui.decimationButton, "decimation"),
      ...]
    slicer.util.addParameterEditWidgetConnections(self.parameterEditWidgets, self.updateParameterNodeFromGUI)

  def updateGUIFromParameterNode(self, caller=None, event=None):
    if self._parameterNode is None or self._updatingGUIFromParameterNode:
      return
    self._updatingGUIFromParameterNode = True
    slicer.util.updateParameterEditWidgetsFromNode(self.parameterEditWidgets, self._parameterNode)
    self._updatingGUIFromParameterNode = False

  def updateParameterNodeFromGUI(self, caller=None, event=None):
    if self._parameterNode is None or self._updatingGUIFromParameterNode:
      return
    wasModified = self._parameterNode.StartModify()  # Modify all properties in a single batch
    slicer.util.updateNodeFromParameterEditWidgets(self.parameterEditWidgets, self._parameterNode)
    self._parameterNode.EndModify(wasModified)
```

--------------------------------

### Configure with Qt6_DIR for Qt Company installer

Source: https://slicer.readthedocs.io/en/latest/developer_guide/build_instructions/linux.html

Sets Qt6_DIR to the Qt Company online installer location for Qt6.

```bash
cmake \
  -DCMAKE_BUILD_TYPE:STRING=Release \
  -DQt6_DIR:PATH=/opt/qt/6.8.0/gcc_64/lib/cmake/Qt6 \
  ../Slicer
```

--------------------------------

### Analyze segmentation fault for installed Slicer with GDB

Source: https://slicer.readthedocs.io/en/latest/developer_guide/debugging/linuxcpp.html

For an installed Slicer, enable core dumps, run Slicer, then use --launch bash to start a shell and run GDB on the SlicerApp-real binary.

```bash
$ ulimit -c unlimited
$ ./Slicer
... make it crash
$ ./Slicer --launch bash
$ gdb ./bin/SlicerApp-real
(gdb) core core
(gdb) backtrace
...
```

--------------------------------

### slicer.ScriptedLoadableModule.ScriptedLoadableModuleTest.setUp()

Source: https://slicer.readthedocs.io/en/latest/genindex.html

Sets up the test environment. This method is part of the ScriptedLoadableModuleTest class and is used to prepare for test execution.

```APIDOC
## setUp()

### Description
Sets up the test environment.

### Class
slicer.ScriptedLoadableModule.ScriptedLoadableModuleTest

### Method
setUp()

### Parameters
No parameters documented.

### Returns
No return value documented.
```

--------------------------------

### Configure CMake with Qt6_DIR for Slicer build

Source: https://slicer.readthedocs.io/en/latest/developer_guide/build_instructions/linux.html

Sets the CMake variable Qt6_DIR to the Qt6 installation path ending with 6.8.0/gcc_64/lib/cmake/Qt6. Also sets Slicer_REQUIRED_QT_VERSION to 6.4. Example assumes Qt is installed in /opt/qt.

```bash
cmake \
  -DCMAKE_BUILD_TYPE:STRING=Release \
  -DSlicer_REQUIRED_QT_VERSION=6.4 \
  -DQt6_DIR:PATH=/opt/qt/6.8.0/gcc_64/lib/cmake/Qt6 \
  ../Slicer
```

--------------------------------

### Set Xcode as active developer directory and accept license

Source: https://slicer.readthedocs.io/en/latest/developer_guide/build_instructions/macos.html

Configures the full Xcode installation as the active developer directory, accepts the license, and verifies the setup. Only needed if installing full Xcode from the App Store.

```bash
#Set it as the active developer directory
sudo xcode-select --switch /Applications/Xcode.app/Contents/Developer

#Accept the license
sudo xcodebuild -license accept

#Verify
xcodebuild -version
xcode-select -p
#Should return something like: /Applications/Xcode.app/Contents/Developer

```

--------------------------------

### ScriptedLoadableModuleWidget.setup

Source: https://slicer.readthedocs.io/en/latest/developer_guide/slicer.html

Method to set up the module widget.

```APIDOC
## ScriptedLoadableModuleWidget.setup

### Description
Method to set up the module widget.

### Method
setup()

### Parameters
None

### Returns
None
```

--------------------------------

### C++ Class and Method Example with this-> Convention

Source: https://slicer.readthedocs.io/en/latest/developer_guide/style_guide.html

Illustrates the C++ naming convention: member variables start with a capital letter and are accessed with 'this->' in implementations. The example shows a class declaration and its method definition.

```cpp
class Node
{
  Object &Foo();
  Object Bla;
};
Object& Node::Foo()
{
  return this->Bla;
}
```

--------------------------------

### slicer.ScriptedLoadableModule.ScriptedLoadableModuleWidget.setup()

Source: https://slicer.readthedocs.io/en/latest/genindex.html

Sets up the module widget. This method is part of the ScriptedLoadableModuleWidget class and is used to initialize the widget's UI.

```APIDOC
## setup()

### Description
Sets up the module widget.

### Class
slicer.ScriptedLoadableModule.ScriptedLoadableModuleWidget

### Method
setup()

### Parameters
No parameters documented.

### Returns
No return value documented.
```

--------------------------------

### slicer.util.getFirstNodeByName

Source: https://slicer.readthedocs.io/en/latest/developer_guide/slicer.html

Gets the first MRML node whose name starts with the specified name, optionally filtering by class.

```APIDOC
## slicer.util.getFirstNodeByName

### Description
Gets the first MRML node that name starts with the specified name. Optionally specify a classname that must also match.

### Method
Function call

### Signature
`slicer.util.getFirstNodeByName(name, className=None)`

### Parameters
- **name** (str) - The name prefix to match.
- **className** (str, optional) - If provided, the node class must match.

### Returns
The first matching node, or None if not found.
```

--------------------------------

### Slicer launcher configuration file (example wrapper script)

Source: https://slicer.readthedocs.io/en/latest/developer_guide/debugging/linuxcpp.html

Configuration file for the Slicer launcher, defining splash screen settings, application path, extra applications (designer, gnome-terminal, xterm, ddd, gdb), library paths, and environment variables. This is the example wrapper script referenced in the debugging guide.

```ini
[General]
launcherSplashImagePath=/cmn/git/Slicer4/Applications/SlicerQT/Resources/Images/SlicerSplashScreen.png
launcherSplashScreenHideDelayMs=3000
additionalLauncherHelpShortArgument=-h
additionalLauncherHelpLongArgument=--help
additionalLauncherNoSplashArguments=--no-splash,--help,--version,--home,--program-path,--no-main-window

[Application]
path=<APPLAUNCHER_DIR>/bin/./SlicerQT-real
arguments=

[ExtraApplicationToLaunch]

designer/shortArgument=
designer/help=Start Qt designer using Slicer plugins
designer/path=/usr/bin/designer-qt4
designer/arguments=

gnome-terminal/shortArgument=
gnome-terminal/help=Start gnome-terminal
gnome-terminal/path=/usr/bin/gnome-terminal
gnome-terminal/arguments=

xterm/shortArgument=
xterm/help=Start xterm
xterm/path=/usr/bin/xterm
xterm/arguments=

ddd/shortArgument=
ddd/help=Start ddd
ddd/path=/usr/bin/ddd
ddd/arguments=

gdb/shortArgument=
gdb/help=Start gdb
gdb/path=/usr/bin/gdb
gdb/arguments=


[LibraryPaths]
1\path=/cmn/git/Slicer4-sb/VTK-build/bin/.
2\path=/cmn/git/Slicer4-sb/CTK-build/CTK-build/bin/.
3\path=/usr/lib
4\path=/cmn/git/Slicer4-sb/ITKv3-build/bin/.
5\path=/cmn/git/Slicer4-sb/SlicerExecutionModel-build/ModuleDescriptionParser/bin/.
6\path=/cmn/git/Slicer4-sb/teem-build/bin/.
7\path=/cmn/git/Slicer4-sb/LibArchive-install/lib
8\path=<APPLAUNCHER_DIR>/bin/.
9\path=../lib/Slicer-4.0/qt-loadable-modules
10\path=<APPLAUNCHER_DIR>/lib/Slicer-4.0/cli-modules/.
11\path=<APPLAUNCHER_DIR>/lib/Slicer-4.0/qt-loadable-modules/.
12\path=/cmn/git/Slicer4-sb/tcl-build/lib
13\path=/cmn/git/Slicer4-sb/OpenIGTLink-build
14\path=/cmn/git/Slicer4-sb/OpenIGTLink-build/bin/.
15\path=/cmn/git/Slicer4-sb/CTK-build/PythonQt-build/.
16\path=/cmn/git/Slicer4-sb/python-build/lib
17\path=/cmn/git/Slicer4-sb/python-build/lib/python2.6/site-packages/numpy/core
18\path=/cmn/git/Slicer4-sb/python-build/lib/python2.6/site-packages/numpy/lib
size=18

[Paths]
1\path=<APPLAUNCHER_DIR>/bin/.
2\path=/cmn/git/Slicer4-sb/teem-build/bin/.
3\path=/usr/bin
4\path=<APPLAUNCHER_DIR>/lib/Slicer-4.0/cli-modules/.
5\path=/cmn/git/Slicer4-sb/tcl-build/bin
size=5

[EnvironmentVariables]
QT_PLUGIN_PATH=<APPLAUNCHER_DIR>/bin<PATHSEP>/cmn/git/Slicer4-sb/CTK-build/CTK-build/bin<PATHSEP>/usr/lib/qt4/plugins
SLICER_HOME=/cmn/git/Slicer4-sb/Slicer-build
PYTHONHOME=/cmn/git/Slicer4-sb/python-build
PYTHONPATH=<APPLAUNCHER_DIR>/bin<PATHSEP><APPLAUNCHER_DIR>/bin/Python<PATHSEP>/cmn/git/Slicer4-sb/python-build/lib/python2.6/site-packages<PATHSEP><APPLAUNCHER_DIR>/lib/Slicer-4.0/qt-loadable-modules/.<PATHSEP><APPLAUNCHER_DIR>/lib/Slicer-4.0/qt-loadable-modules/Python
TCL_LIBRARY=/cmn/git/Slicer4-sb/tcl-build/lib/tcl8.4
TK_LIBRARY=/cmn/git/Slicer4-sb/tcl-build/lib/tk8.4
TCLLIBPATH=/cmn/git/Slicer4-sb/tcl-build/lib/itcl3.2 /cmn/git/Slicer4-sb/tcl-build/lib/itk3.2
```

--------------------------------

### Install Qt 5 components via command line

Source: https://slicer.readthedocs.io/en/latest/developer_guide/build_instructions/linux.html

Installs the Qt 5.15.2 components required by 3D Slicer (gcc_64, qtwebengine, and qtwebengine.gcc_64) using the Qt online installer. Prompts for license agreements and permissions.

```bash
export QT_ACCOUNT_LOGIN=<set your qt.io account email here>
export QT_ACCOUNT_PASSWORD=<set your password here>
./qt-online-installer-linux-x64-online.run \
  install \
    qt.qt5.5152.gcc_64 \
    qt.qt5.5152.qtwebengine \
    qt.qt5.5152.qtwebengine.gcc_64 \
  --root /opt/qt \
  --email $QT_ACCOUNT_LOGIN \
  --pw $QT_ACCOUNT_PASSWORD
```

--------------------------------

### startQtDesigner() (in module slicer.util)

Source: https://slicer.readthedocs.io/en/latest/genindex.html

Function in slicer.util to start Qt Designer.

```APIDOC
## startQtDesigner()

### Description
Function in slicer.util to start Qt Designer.

### Method
startQtDesigner()

### Parameters
None documented.

### Response
No documented return value.
```

--------------------------------

### pip_ensure example in ScriptedLoadableModuleWidget

Source: https://slicer.readthedocs.io/en/latest/developer_guide/slicer.html

Shows how to use slicer.packaging.pip_ensure to install a package before importing it. The requester parameter identifies the requesting module in the UI. After pip_ensure returns, the package is safe to import and use.

```python
class MyFilterWidget(ScriptedLoadableModuleWidget):

    def onApplyButton(self):
        slicer.packaging.pip_ensure("scikit-image>=0.20", requester="MyFilter")
        import skimage

        # Now safe to use skimage
        filtered = skimage.filters.gaussian(array, sigma=2.0)
```

--------------------------------

### Extension description file syntax example

Source: https://slicer.readthedocs.io/en/latest/developer_guide/extensions.html

Illustrates the syntax of an .s4ext file: comments start with '#', metadata is specified as 'metadataname value', and empty lines are ignored. Multiline values are not supported.

```plaintext
# This is a comment
metadataname This is the value associated with 'metadataname'

# This is an other comment
anothermetadata This is the value associated with 'anothermetadata'
```

--------------------------------

### Install Qt 6 components via command line

Source: https://slicer.readthedocs.io/en/latest/developer_guide/build_instructions/linux.html

Installs the Qt 6.8.0 components required by 3D Slicer (base libraries, Qt WebEngine, and Qt5Compat) using the Qt online installer. Prompts for license agreements and permissions.

```bash
export QT_ACCOUNT_LOGIN=<set your qt.io account email here>
export QT_ACCOUNT_PASSWORD=<set your password here>
./qt-online-installer-linux-x64-online.run \
  install \
    qt.qt6.680.gcc_64 \
    qt.qt6.680.addons.qtwebengine \
    qt.qt6.680.addons.qt5compat \
  --root /opt/qt \
  --email $QT_ACCOUNT_LOGIN \
  --pw $QT_ACCOUNT_PASSWORD
```

--------------------------------

### Accessing a public member function in Python

Source: https://slicer.readthedocs.io/en/latest/developer_guide/api.html

Shows how to call a public member function of a VTK object from Python, using the example of getting the number of nodes of a specific class from the scene.

```python
slicer.mrmlScene.GetNumberOfNodesByClass('vtkMRMLTransformNode')
```

--------------------------------

### Start markups control point placement via selection and interaction nodes

Source: https://slicer.readthedocs.io/en/latest/developer_guide/script_repository/markups.html

Lower-level approach: sets the active place node class to vtkMRMLMarkupsFiducialNode and sets the interaction mode to Place (mode 1) with persistence.

```Python
selectionNode = slicer.mrmlScene.GetNodeByID("vtkMRMLSelectionNodeSingleton")
selectionNode.SetReferenceActivePlaceNodeClassName("vtkMRMLMarkupsFiducialNode")
interactionNode = slicer.mrmlScene.GetNodeByID("vtkMRMLInteractionNodeSingleton")
placeModePersistence = 1
interactionNode.SetPlaceModePersistence(placeModePersistence)
# mode 1 is Place, can also be accessed via slicer.vtkMRMLInteractionNode().Place
interactionNode.SetCurrentInteractionMode(1)
```

--------------------------------

### Set a new default module at startup using QSettings

Source: https://slicer.readthedocs.io/en/latest/developer_guide/script_repository/gui.html

Changes the default module from Welcome to Data by setting the 'Modules/HomeModule' setting.

```python
qt.QSettings().setValue("Modules/HomeModule", "Data")
```
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