Ratio of a recording's average frame peak to its average frame mean. A PCI of 1 would mean a perfectly uniform mat; the larger the value, the more of the load sits under a single hotspot.
Usage
pr_calc_pci(trial, denominator = c("grid", "loaded"), eps = 1e-12)Arguments
- trial
A pr_trial object.
- denominator
Character.
"grid"(default) or"loaded"; see Details.- eps
Numeric. Added to the mean-pressure denominator. Default
1e-12.
Details
PCI = mean(peak_kPa) / mean(mean_kPa) — a ratio of two per-recording
averages, not the average of a per-frame ratio; the two differ whenever
load varies over time, and the cohort summaries use the former.
denominator selects which mean goes underneath:
"grid"(default) usespr_calc_mean_pressure_grid(), the whole-grid mean including unloaded cells. This is the cohort definition and the one whose interpretation bandspr_ref_pci()documents."loaded"uses the loaded-cells-only mean ofpr_calc_mean_pressure(), which is a different quantity — that function is loaded-cells-only by definition and is untouched here. Values come out roughly an order of magnitude smaller on a sparsely loaded mat, andpr_ref_pci()does not apply to them.
eps guards the denominator so a recording with no load at all returns
0 instead of NaN.
See also
Other whole-grid frame metrics:
pr_calc_cop_grid(),
pr_calc_loaded_count(),
pr_calc_mean_pressure_grid(),
pr_calc_total_pressure(),
pr_frame_metrics(),
pr_ref_pci()
Examples
trial <- pr_example_trial("saddle_horse")
pr_calc_pci(trial)
#> [1] 10.11783
# The loaded-cells-only denominator is larger, so the index is smaller:
pr_calc_pci(trial, denominator = "loaded") < pr_calc_pci(trial)
#> [1] TRUE