Point ↔ cell data averaging

point_data_to_cell_data and cell_data_to_point_data move data between locations without changing the geometry. They are data operations, not file formats.

• point → cell: each cell's value is the mean over its own nodes.
• cell → point: each point's value is the mean over the cells incident to it, optionally weighted by each cell's |measure|.

import meshioplusplus as mp

mesh = mp.read("part.vtu")

# Every point_data array becomes a cell_data array of the same name.
cells = mp.point_data_to_cell_data(mesh)

# Only the named arrays, written under a suffixed name.
cells = mp.point_data_to_cell_data(mesh, keys=["T", "p"], suffix="_c")

# Cell -> point, weighted by cell area/volume so large cells count for more.
points = mp.cell_data_to_point_data(mesh, keys=["stress"], weighted=True)

Weighting

weighted=False (the default) counts every incident cell equally. weighted=True weights each contribution by the cell's |measure| — length for a 1D cell, area for a 2D cell, volume for a 3D one. On a mesh with cells of very different sizes the two differ substantially; on a uniform mesh they coincide.

Cells whose measure cannot be computed — ragged polygon and polyhedron blocks — fall back to a unit weight, with one warning per call.

Components and data types

Both directions work component-wise, so scalar, vector and tensor arrays are handled identically. A scalar array stays 1-D; a vector array keeps its (n, ncomp) shape.

The output is always float64, whatever the input dtype: the mean of an int32 field is not an int32.

Edge cases

• A point touched by no cell — or by no cell carrying a finite value — yields NaN. So does a cell whose nodes all carry non-finite values.
• Non-finite values never contribute to an average. See the NaN policy.
• Ragged polygon blocks average over the row's nodes; polyhedron blocks average over the distinct nodes across all of a cell's faces.

Determinism

The cell → point direction is a scatter, and floating-point addition is not associative, so its accumulation pass runs serially on purpose: the result must not depend on the thread count. Only the final divide is parallelised.

CLI

meshioplusplus data to-cell  in.vtu out.vtu --keys T,p --target-suffix _c
meshioplusplus data to-point in.vtu out.vtu --keys stress --weighted

Omit --keys to convert every array at the source location. See the CLI reference.

Other languages

• C API — mio_data_point_to_cell(mesh, names, count, suffix) and mio_data_cell_to_point(mesh, names, count, weight, suffix), where weight is MIO_WEIGHT_UNIFORM or MIO_WEIGHT_MEASURE. Pass count == 0 for "every array". See the C API reference.
• Fortran — m%data_point_to_cell() and m%data_cell_to_point(["stress"], weight=MIO_WEIGHT_MEASURE). See the Fortran reference.
• WebAssembly / JavaScript — dataPointToCell(mesh, ["T"], "_c") and dataCellToPoint(mesh, ["stress"], "measure", ""). See the WebAssembly reference.