How to export result of point_metrics() in lidR?

Question

I have las files along coastal areas which include multiple flights. Usually I use both water and ground when normalizing but this data has 2 things to overcome. The first has ground at a lower level than water due to tides. The second is a problem because one flight classified vegetation as water. To help solve this (a quick attempt at ground classification didn't quite work), I want to extract water and ground, and then use point_metrics() to get the minimum value within a small neighbourhood. The idea is to use this minimum value as ground during normalization. How can I export the results of point_metrics() data table to a raster or las file (it has pointId & V1)?

[![profile of las with classification][1]][1]

library(raster)
setwd('D:/test/las')
las <- readLAS('579_4998_201801.las', filter = "-keep_class 2 9")
lasmin <- point_metrics(las, func = ~min(Z), k = 2, r = 1)


  [1]: https://i.sstatic.net/7bsmC.png

Answer 1

There are plenty of options depending on what you really want to do.

You can keep only the points with min Z that way

library(lidR)
f = system.file("extdata", "Topography.laz", package="lidR")
las = readLAS(f, filter = "-keep_class 2 9")
min = point_metrics(las, func = ~list(minZ = min(Z)), k = 2, r = 1)
boo = min$minZ == las$Z                    
gnd = las[boo]

If you want to get XYZ there is an option for that:

min = point_metrics(las, func = ~list(minZ = min(Z)), k = 2, r = 1, xyz = TRUE)

If you want to reclassify the points based on the output of point_metrics() this is also doable but a little bit harder.