Calculate per-segment centers of mass

Lower-level function that computes the center of mass for individual body segments from marker position data.

Usage

calculateSegmentCOM(pe, proximal_markers, distal_markers, com_fractions)

Arguments

pe

A PhysioExperiment object with position_x, position_y, and optionally position_z assays.

proximal_markers

Character vector of proximal marker names, one per segment.

distal_markers

Character vector of distal marker names, one per segment (same length as proximal_markers).

com_fractions

Numeric vector of COM proximal fractions (0-1), one per segment (same length as proximal_markers).

Value

A named list of matrices, one per segment. Each matrix has dimensions (n_frames x 2) for 2D data or (n_frames x 3) for 3D data, with columns named "x", "y", and (optionally) "z".

References

Winter DA (2009). "Biomechanics and Motor Control of Human Movement." 4th ed. John Wiley & Sons.

See also

calculateCOM() for whole-body center of mass, segmentParameters() for body segment inertial parameters.

Examples

n <- 50
mk <- function(v) { m <- matrix(v, n, 3); colnames(m) <- c("A", "B", "C"); m }
pe <- PhysioExperiment(
  assays = S4Vectors::SimpleList(position_x = mk(1), position_y = mk(2),
                                 position_z = mk(0)),
  colData = S4Vectors::DataFrame(label = c("A", "B", "C"),
                                 type = rep("marker", 3)),
  samplingRate = 100)
seg_com <- calculateSegmentCOM(pe, proximal_markers = "A",
  distal_markers = "B", com_fractions = 0.5)
names(seg_com)
#> [1] "A_to_B"
head(seg_com[[1]])
#>      x y z
#> [1,] 1 2 0
#> [2,] 1 2 0
#> [3,] 1 2 0
#> [4,] 1 2 0
#> [5,] 1 2 0
#> [6,] 1 2 0