When using by_echo in any of the _metrics() functions the metrics calculated for the lastofmany echoes are NA.
Here is an example using some functions:
LASfile <- system.file("extdata", "Megaplot.laz", package="lidR")
las <- readLAS(LASfile, filter = "-keep_random_fraction 0.5")
echo = c("all", "first", "intermediate", "lastofmany", "single", "multiple")
# ================
# CLOUD METRICS
# ================
m = cloud_metrics(las, .stdmetrics_z, by_echo = echo)
col = names(m)[grepl("zmax", names(m))]
unlist(m[col])
#> zmax zmax.first zmax.intermediate zmax.lastofmany zmax.single zmax.multiple
#> 29.97 29.97 24.01 NA 29.97 28.56
# ================
# PIXEL METRICS
# ================
m <- pixel_metrics(las, .stdmetrics_z, 20, by_echo = echo)
col = names(m)[grepl("zmax", names(m))]
unlist(m[col])
#> class : SpatRaster
#> dimensions : 13, 12, 6 (nrow, ncol, nlyr)
#> resolution : 20, 20 (x, y)
#> extent : 684760, 685000, 5017760, 5018020 (xmin, xmax, ymin, ymax)
#> coord. ref. : NAD83 / UTM zone 17N (EPSG:26917)
#> sources : memory
#> memory
#> memory
#> ... and 3 more source(s)
#> names : zmax, zmax.first, zmax.~diate, zmax.~fmany, zmax.single, zmax.~tiple
#> min values : 0.00, 0.00, 5.36, NaN, 0.00, 10.88
#> max values : 29.97, 29.97, 24.01, NaN, 29.97, 28.56
# ================
# PLOT METRICS
# ================
shpfile <- system.file("extdata", "efi_plot.shp", package="lidR")
inventory <- sf::st_read(shpfile, quiet = TRUE)
m <- plot_metrics(las, .stdmetrics_z, inventory, radius = 11.28,by_echo = echo)
col = names(m)[grepl("zmax", names(m))]
summary(m[,col])
#> zmax zmax.first zmax.intermediate zmax.lastofmany zmax.single zmax.multiple geometry
#> Min. :21.61 Min. :21.61 Min. :14.92 Min. : NA Min. :21.15 Min. :21.61 POINT :5
#> 1st Qu.:25.26 1st Qu.:25.26 1st Qu.:18.26 1st Qu.: NA 1st Qu.:25.26 1st Qu.:23.25 epsg:26917 :0
#> Median :25.26 Median :25.26 Median :19.05 Median : NA Median :25.26 Median :24.60 +proj=utm ...:0
#> Mean :24.84 Mean :24.84 Mean :18.71 Mean :NaN Mean :24.73 Mean :24.13
#> 3rd Qu.:25.89 3rd Qu.:25.89 3rd Qu.:20.41 3rd Qu.: NA 3rd Qu.:25.89 3rd Qu.:25.03
#> Max. :26.18 Max. :26.18 Max. :20.89 Max. : NA Max. :26.11 Max. :26.18 NA's :5
# ================
# CROWN METRICS
# ================
# Already tree-segmented point cloud
LASfile <- system.file("extdata", "MixedConifer.laz", package="lidR")
trees <- readLAS(LASfile, filter = "-drop_z_below 0")
metrics <- crown_metrics(trees, .stdtreemetrics, by_echo = echo)
col = names(metrics)[grepl("Z.", names(metrics))]
summary(metrics[,col]) # Here also "intermediate" echoes return NA metrics
#> Z.first Z.intermediate Z.lastofmany Z.single Z.multiple geometry
#> Min. : 2.76 Min. : NA Min. : NA Min. : 2.76 Min. : 4.24 POINT Z :200
#> 1st Qu.:19.09 1st Qu.: NA 1st Qu.: NA 1st Qu.:18.80 1st Qu.:17.42 epsg:26912 : 0
#> Median :21.59 Median : NA Median : NA Median :21.55 Median :20.41 +proj=utm ...: 0
#> Mean :21.03 Mean :NaN Mean :NaN Mean :20.90 Mean :19.86
#> 3rd Qu.:24.08 3rd Qu.: NA 3rd Qu.: NA 3rd Qu.:24.08 3rd Qu.:22.62
#> Max. :32.07 Max. : NA Max. : NA Max. :32.07 Max. :31.94
#> NA's :200 NA's :200 NA's :2
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