Add note about VTKHDF change to docs

docs/source/features.rst

@@ -67,3 +67,12 @@ Open source, robust, file formats
 Alongside improvements to the input file there is a new output file format – `HDF5 <http://www.hdfgroup.org/HDF5/>`_ – to manage the larger and more complex data sets that are being generated. HDF5 is a robust, portable and extensible format with a number of free readers available. For further details see the :ref:`Simulation Output <output>` section.
 
 In addition, the `Visualization Toolkit (VTK) <http://www.vtk.org>`_ is being used for improved handling and viewing of the detailed 3D FDTD geometry meshes. The VTK is an open-source system for 3D computer graphics, image processing and visualisation. It also has a number of free readers available including `Paraview <http://www.paraview.org>`_. For further details see the :ref:`geometry view command <geometryview>`.
+
+.. note::
+
+    As of June 2025, gprMax uses the `VTKHDF file format
+    <https://docs.vtk.org/en/latest/design_documents/VTKFileFormats.html#vtkhdf-file-format>`_
+    rather than the previous `XML file format
+    <https://docs.vtk.org/en/latest/design_documents/VTKFileFormats.html#xml-file-formats>`_
+    in order to better support parallel I/O. The Paraview macro has been
+    updated to reflect this change.

docs/source/output.rst

@@ -137,9 +137,9 @@ The following are steps to get started with viewing snapshot files in Paraview:
 Geometry output
 ===============
 
-Geometry files use the open source `Visualization ToolKit (VTK) <http://www.vtk.org>`_ format which can be viewed in many free readers, such as `Paraview <http://www.paraview.org>`_. Paraview is an open-source, multi-platform data analysis and visualization application. It is available for Linux, Mac OS X, and Windows.
+Geometry files use the open source `Visualization ToolKit (VTK) <http://www.vtk.org>`_ format (specifically VTKHDF) which can be viewed in many free readers, such as `Paraview <http://www.paraview.org>`_. Paraview is an open-source, multi-platform data analysis and visualization application. It is available for Linux, Mac OS X, and Windows.
 
-The ``#geometry_view:`` command produces either ImageData (.vti) for a per-cell geometry view, or UnstructuredGrid (.vtu) for a per-cell-edge geometry view. The following are steps to get started with viewing geometry files in Paraview:
+The ``#geometry_view:`` command produces either ImageData for a per-cell geometry view, or UnstructuredGrid for a per-cell-edge geometry view. The following are steps to get started with viewing geometry files in Paraview:
 
 .. _pv_toolbar:
 

gprMax/snapshots.py

@@ -237,7 +237,7 @@ class Snapshot(Generic[GridType]):
         )
 
     def write_file(self, pbar: tqdm):
-        """Writes snapshot file either as VTK ImageData (.vti) format
+        """Writes snapshot file either as VTK ImageData (.vtkhdf) format
             or HDF5 format (.h5) files
 
         Args:

gprMax/user_objects/cmds_output.py

@@ -49,7 +49,7 @@ class Snapshot(OutputUserObject):
                             must be specified for point in time at which the
                             snapshot will be taken.
         fileext: optional string to indicate type for snapshot file, either
-                            '.vti' (default) or '.h5'
+                            '.vtkhdf' (default) or '.h5'
         outputs: optional list of outputs for receiver. It can be any
                     selection from Ex, Ey, Ez, Hx, Hy, or Hz.
     """