Mean pressure across the entire sensor grid for each frame: the frame sum divided by the number of sensors, with unloaded cells counted as zeros.
Arguments
- trial
A pr_trial object.
Details
This is deliberately not the same quantity as pr_calc_mean_pressure(),
which averages only the cells above threshold (loaded-cells-only, by
definition) and is left untouched. On a saddle mat where a typical frame
loads roughly 4% of the 256 cells, the loaded-cells-only mean is around
25 times the whole-grid mean, so the two are never interchangeable. Use
this one when the mat itself is the region of interest and an unloaded
cell is a real "no pressure here" measurement; use
pr_calc_mean_pressure() when the sensor sheet is larger than the loaded
object and only the contact patch is meaningful.
The denominator is trial$layout$n_sensors, i.e. the number of active
sensors, which equals ncol(trial$pressure). Inactive grid cells are not
measurements and never enter the average.
See also
Other whole-grid frame metrics:
pr_calc_cop_grid(),
pr_calc_loaded_count(),
pr_calc_pci(),
pr_calc_total_pressure(),
pr_frame_metrics(),
pr_ref_pci()
Examples
trial <- pr_example_trial("saddle_horse")
grid_mean <- pr_calc_mean_pressure_grid(trial)
loaded_mean <- pr_calc_mean_pressure(trial)
# The whole-grid mean is the smaller of the two by construction:
all(grid_mean <= loaded_mean + 1e-9)
#> [1] TRUE