fVTKHDF

A modern Fortran library for writing VTKHDF format files.

This library provides a high-level, object-oriented Fortran interface for generating VTKHDF files, a relatively new HDF5-based VTK file format used by ParaView. The library is designed for high-performance computing (HPC) applications, offering robust MPI-parallel output via HDF5, while also supporting serial workflows. By utilizing HDF5 as the underlying storage mechanism, fVTKHDF provides a more scalable alternative to older VTK ASCII or XML formats.

• Targets version 2.5 of the VTKHDF File Format Specification.
• ParaView 5.13+ recommended for full support of the generated files.

Dataset Support

fVTKHDF currently supports the following VTK data models:

• UnstructuredGrid (UG): For meshes with arbitrary cell types (tetrahedrons, hexahedrons, etc.).

  • Supports a static mesh (fixed geometry and topology) with both static and temporal data.

  • Supports point-centered, cell-centered, and field data.

• MultiBlockDataSet (MB): Supports a flat assembly/collection of UnstructuredGrid blocks (leaf nodes).

  • Hierarchical assembly of MultiBlock datasets is not supported.

  • Ideal for a logical decomposition of a model into distinct components (e.g., piston, cylinder, valves), independent of any parallel domain decomposition.

Documentation

See the Reference Manual.

Installation

Prerequisites

• Fortran 2018 Compiler (GCC 13+, Intel oneAPI, etc.)
• CMake (3.28+)
• HDF5 Library (1.10+)
• Python 3 + fypp (pip install fypp)
• MPI (Optional)

Build and Install

By default, the library builds with MPI support enabled. Use -DENABLE_MPI=OFF for a serial-only build.

git clone https://github.com/nncarlson/fvtkhdf
cd fvtkhdf
# Configure the build and set install location
cmake -B build --install-prefix /path/to/install
# Build and install
cmake --build build --parallel
cmake --install build

Using fVTKHDF in your Project

Once installed, you can use fVTKHDF in your own CMake-based project by adding the following to your CMakeLists.txt:

find_package(fVTKHDF REQUIRED)

add_executable(my_simulation main.f90)
target_link_libraries(my_simulation PRIVATE fVTKHDF::fvtkhdf)

Quick Start

Here is a minimal serial example that writes a VTKHDF UnstructuredGrid dataset for an unstructured mesh consisting of a single tetrahedral cell with a scalar field. More complete examples (serial and MPI-parallel, UnstructuredGrid and MultiBlockDataSet) are provided in the examples directory.

program quick_start

  use,intrinsic :: iso_fortran_env, only: int8
  use vtkhdf_ug_file_type
  use vtkhdf_vtk_cell_types, only: VTK_TETRA
  implicit none

  ! 1. Declare the file object (Unstructured Grid)
  type(vtkhdf_ug_file) :: myfile

  ! Data arrays
  real, allocatable :: points(:,:)
  integer, allocatable :: cnode(:), xcnode(:)
  integer(int8), allocatable :: types(:)
  real, allocatable :: temperature(:)

  integer :: stat
  character(:), allocatable :: errmsg

  ! 2. Define a simple Tetrahedron (4 points, 1 cell)
  points = reshape([real :: 0,0,0,  1,0,0,  0,1,0,  0,0,1], [3,4])
  cnode = [1, 2, 3, 4] ! cell-node connectivity
  xcnode = [1, 5]      ! cnode start index of connectivity list
  types = [VTK_TETRA]
  temperature = [100.0, 200.0, 300.0, 400.0] ! Point data

  ! 3. Create and Write
  call myfile%create("simple.vtkhdf", stat, errmsg)
  if (stat /= 0) error stop errmsg

  ! Write the mesh topology (Static Mesh)
  call myfile%write_mesh(points, cnode, xcnode, types)

  ! Write a data field
  call myfile%write_point_data("Temperature", temperature)

  call myfile%close()

end program quick_start

Development Roadmap

Planned and prospective features include:

• Completing UnstructuredGrid (UG) feature coverage

  • Add support for temporal mesh:
    • geometry only
    • geometry and topology
  • Add support for polyhedron cells

• Composite VTK datasets

  • Replace MB with PartitionedDataSetCollection (PDC) (issue #26)
  • Implement a general Assembly tree for PDC to replace the existing flat tree.

• New features added in VTKHDF version 2.6

  • Add support for Attribute data on cell/point/field datasets (issue #23).

Additional Dataset Types

The VTKHDF format specification defines the format for additional VTK dataset types (e.g., HyperTreeGrid, OverlappingAMR, etc.) that are not currently supported.

Contributions adding support for these formats are very welcome. I am happy to collaborate on design and integration so that new functionality fits naturally within the existing API and internal infrastructure.

If you are interested in contributing support for one of these dataset types, please open an issue to discuss design and implementation details.

License

fVTKHDF is distributed under the 2-clause BSD license. See LICENSE.md for details.