VTK ImageData#

.vti read + write eager

Summary of the specification#

.vti is the XML serial form of a VTK ImageData: a uniform grid stored entirely as metadata. A <VTKFile type="ImageData"> root holds an <ImageData> carrying WholeExtent, Origin and Spacing — the index range on each axis, the coordinate of the first node, and the constant step between nodes. There are no coordinates in the file at all; every node position follows from origin + index * spacing, and the cells are the hexahedra implied by the extent. Only <PointData> and <CellData> arrays carry actual payload, encoded like any other VTK XML file.

Specification at a glance#

root	<VTKFile type=”ImageData”>
extent	WholeExtent=”i0 i1 j0 j1 k0 k1”
geometry	Origin + Spacing; no coordinate array
connectivity	implicit; cells follow from the extent
encodings	ascii, base64, appended (raw or base64), optionally zlib-compressed

Read the full VTK XML specification ↗

Reading#

import polyxios as px

mesh = px.read("volume.vti")
mesh.vertices          # materialised from origin + index * spacing

Writing#

px.write(mesh, "out.vti")                 # base64 payloads (default)
px.write(mesh, "out.vti", binary=False)   # inline ASCII

option	meaning
`binary`	`True` (the default) writes base64-encoded payloads; `False` writes inline ASCII.

Quirks worth knowing#

Both the coordinates and the connectivity are materialised on read. A file of a few hundred bytes can expand to a large in-memory mesh, because the extent is all it takes to describe one.
Origin defaults to 0 0 0 and Spacing to 1 1 1 when the attributes are absent.
A <Piece> may restate a sub-extent of WholeExtent; the piece’s own extent is what gets expanded.
lazy=True raises LazyReadError.