lidR custom grid metric returning raster output mean max values lower than 1 m for mean height bin interval between 0.2-4

Question

I want to calculate the mean height of shrubs layer using the mean height of points between 0.2-4 m above ground but the raster output mean max values never is higher than 1 m which is not make sense since we have areas with mean shrubs higher than 2 m at 15 x 15 m pixel resolution.

The code I used to generate the metric

mean_shrub_height = function(z) {
  SH=mean(z >= 0.2 & z <= 4)
  return(list(SH =SH))
}

mean_shrub_height = grid_metrics(las, ~mean_shrub_height(Z), res = 15)

Answer 1

You are computing the mean of a boolean vector which is indeed between 0 and 1.

One solution

msh = function(z) {
  z = z[z >= 0.2 & z <= 4]
  SH=mean(z)
  return(list(SH =SH))
}

Another option

msh = pixel_metrics(las, ~list(SH = mean(Z)), res = 15, filter = ~Z >= 0.2 & Z <= 4)