Write a C3D Motion Capture File

Writes 3D marker trajectories (and optional analog channels) from a PhysioExperiment to a binary C3D file via the c3dr package. This is the inverse of readC3D(): a readC3D() -> writeC3D() -> readC3D() round-trip reproduces the marker coordinates (within 32-bit float precision) and preserves the point/analog sampling-rate ratio.

Usage

writeC3D(x, path, include_analog = TRUE)

Arguments

x

A PhysioExperiment with "position_x", "position_y", and "position_z" assays (as produced by readC3D() or readTRC()), or a MultiRatePhysioExperiment whose marker stream carries those assays.

path

Character string giving the output .c3d path.

include_analog

Logical; if TRUE (default) and the object carries analog data (in metadata(x)$analog_data, or as an "analog" stream of a MultiRatePhysioExperiment), that data is written as C3D analog channels. If FALSE, a marker-only C3D file is written.

Value

The output path, invisibly.

Details

The point (marker) rate is taken from samplingRate(x). When analog data is written, the analog rate and the integer point/analog ratio (ANALOG:RATE / POINT:RATE, i.e. analog subframes per point frame) are derived from the analog block so the ratio round-trips exactly. Force platform metadata is not written (the marker and analog signals are preserved; force-plate corner/calibration parameters are dropped).

References

C3D.org. "The C3D File Format." https://www.c3d.org/.

See also

readC3D(), writeTRC(), writeMOT()

Examples

if (requireNamespace("c3dr", quietly = TRUE)) {
  pe <- readC3D(c3dr::c3d_example(), include_analog = TRUE)
  out <- tempfile(fileext = ".c3d")
  writeC3D(pe, out)
  pe2 <- readC3D(out)
}