Vtu

VTU refers to the VTK Unstructured Grid XML file format used by the Visualization Toolkit (VTK) to store unstructured grid data. The .vtu file format provides a self-describing, platform-independent way to exchange simulation results and visualization data between VTK-based applications such as ParaView, Visit, and various in-house tools. It is part of the VTK XML family, which standardized data storage with a readable XML wrapper around numerical arrays.

A VTU file begins with a VTKFile element that specifies the type as UnstructuredGrid, along with a version and byte order. The primary dataset is an UnstructuredGrid element that contains Points, Cells, and optional data blocks. Points holds the 3D coordinates of mesh nodes. Cells describes the mesh topology through connectivity information, including offsets and cell types. PointsData and CellData store per-point and per-cell attributes (for example, scalars, vectors, tensors). FieldData can hold global attributes for the dataset.

Data within a VTU file is carried by DataArray elements. Each DataArray has attributes such as name, type (e.g., Float32, Float64, Int32), and NumberOfComponents. Data can be stored in ASCII or binary form; for large datasets, the appended data approach is commonly used, where the actual numerical data is kept in a separate binary block while the XML contains references to it.

VTU files are widely used in serial and parallel workflows. In parallel workflows, multiple VTU blocks can be combined via a PVTU index file, enabling distributed reading and processing. The format supports various data modalities and is compatible with many visualization and post-processing toolchains.