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Per-Frame Metric Table

Source: R/frame-metrics.R
pr_frame_metrics.Rd

Computes the whole-grid frame vocabulary — mean, peak, total, loaded cell count and grid-index centre of pressure — in a single vectorised pass over the pressure matrix.

Usage

pr_frame_metrics(trial, threshold = 0, eps = 1e-12)

Arguments

trial

A pr_trial object.

threshold

Numeric. Cells at or below this value count as unloaded. Default 0.

eps

Numeric. Added to the weight sum to keep unloaded frames finite. Default 1e-12.

Value

A tibble::tibble with n_frames rows and columns frame, time_s, mean_kPa, peak_kPa, total_kPa, loaded, cop_row, cop_col. Pressure columns carry the trial's own unit; the kPa suffixes follow the cohort naming convention.

Details

Every column is computed with whole-matrix operations — two rowSums(), one max.col(), and a single matrix product carrying both COP axes. There is no per-frame R loop, because cohort-scale inputs run to millions of frames. Measured on a 200,000 x 256 matrix (R 4.6.1, one core): about 145,000 frames per second, i.e. roughly 70 s for a 5.5 M-frame cohort, against 73-83 s for the equivalent vapply() over rows. The default threshold = 0 also skips masking the matrix entirely when no reading is negative, which saves a full copy of the pressure data.

Column definitions:

  • mean_kPa — total_kPa / n_sensors, whole grid, zeros included. This is not pr_calc_mean_pressure(), which is loaded-cells-only by definition and is left unchanged; see pr_calc_mean_pressure_grid().

  • peak_kPa — the plain row maximum, not filtered by threshold.

  • total_kPa — the plain row sum, not filtered by threshold.

  • loaded — count of cells strictly above threshold.

  • cop_row, cop_col — grid index units, eps on the denominator so an unloaded frame gives approximately 0 rather than NA.

threshold therefore affects loaded and the COP weighting only; peak and total always describe the frame as recorded.

See also

Other whole-grid frame metrics: pr_calc_cop_grid(), pr_calc_loaded_count(), pr_calc_mean_pressure_grid(), pr_calc_pci(), pr_calc_total_pressure(), pr_ref_pci()

Examples

trial <- pr_example_trial("saddle_horse")
fm <- pr_frame_metrics(trial)
names(fm)
#> [1] "frame"     "time_s"    "mean_kPa"  "peak_kPa"  "total_kPa" "loaded"   
#> [7] "cop_row"   "cop_col"  
all.equal(fm$mean_kPa, fm$total_kPa / trial$layout$n_sensors)
#> [1] TRUE