Field Data¶

Field data consists of values associated with a simple VTK dataset as a whole rather than with its mesh points or cells. All writers for simple VTK datasets provide the interface described here. Field data writes need not be ordered with respect to mesh writes. Static field data may be written at any point after file creation and before closing the file; temporal field data is written within its corresponding time step.

In the signatures below, file denotes a file writer object for a simple VTK dataset; see Overview for the available writer types and their modules.

Values and Interpretation¶

The array argument may be a scalar, a rank-1 array, or a rank-2 array of kind int32, int64, real32, or real64. The kind constants are available from iso_fortran_env.

VTK and ParaView interpret these values as tuples with one or more components:

Fortran argument	Number of tuples	Components per tuple
Scalar	1	1
Rank-1 `array(n)`	`n`	1
Rank-1 `array(n)`, `as_vector=.true.`	1	`n`
Rank-2 `array(ncomp,ntuples)`	`ntuples`	`ncomp`

as_vector is optional and defaults to false. It may be true only for rank-1 arguments. It changes the grouping into components and tuples; it does not require three components or assign a geometric vector role. For a rank-2 argument, each Fortran column is one tuple.

In MPI builds, all field data calls are collective. All ranks must supply matching argument types, kinds, and shapes. Only rank zero contributes the written values; values on other ranks are never referenced.

Note

String-valued field data is not currently supported by fVTKHDF due to incompatibilities between parallel HDF5 writing and VTK’s string reading.

Static Field Data¶

call file%write_field_data(name, array [, as_vector])

Write a complete static field dataset.

name: character name, handled according to Common Conventions.
array: complete scalar or array value, interpreted as described above.
as_vector: optional logical controlling rank-1 interpretation.

Static field data is allowed in every writer mode. Each call creates a new field, including when a name is repeated. No handle is returned, and writes are not incremental.

In a temporal file, the value applies to every step. It may be written before time stepping, during or between steps, or after the last step has been finalized and before closing the file. Values written later also apply to earlier steps. No temporal registration is required.

Temporal Field Data¶

type(vtkhdf_field_data_handle) :: field_var

field_var = file%register_temporal_field_data(name, mold)

name: character name, handled according to Common Conventions.
mold: scalar determining the numeric type and kind. Its value is ignored. It does not constrain the rank, shape, or component count of later writes.

Registration is allowed only in a temporal mode and must precede the first call to start_time_step.

call file%write_field_data(field_var, array [, as_vector])

Write the complete value for the current time step to the registered field.

field_var: handle returned by registration.
array: scalar or array with the registered type and kind.
as_vector: optional logical controlling rank-1 interpretation.

A time step must be open. Each field may be written at most once per step. The rank, extents, and number of components may change between steps.

If a field is omitted from a step, its most recently written value is reused. Before the first write, omission gives an empty field for that step. These rules are independent of the first-step requirements for point and cell data.

Example¶

The following calls write three scalar tuples and one three-component tuple, respectively, in a static file:

call file%write_field_data('values', [1.0,2.0,3.0])
call file%write_field_data('direction', [1.0,0.0,0.0], as_vector=.true.)