Plot a 2D Canopy Height Model (CHM) line

Question

I'm looking for some help creating a "Canopy Height Model (CHM)-Zmax-curve/line" on my las-plots. I extracted a transect with the lidR package

las_tr <- clip_transect(las, p1, p2, width = 3, xz=T)

And I plotted it with ggplot

ggplot(las_tr@data, aes(X,Z, color = Z)) +
     geom_point(size = 0.5) + 
     coord_equal() + 
     theme_minimal() +
     scale_color_gradientn(colours = height.colors(50)) +
     xlim(-80,0) + ylim(0,45) +
     labs(title = "2D profile", subtitle= paste(round(x[i]),round(y[i])))

I have this

But I would like something like this

I hope someone can help me.

Answer 1

library(lidR)
library(dplyr)
library(ggplot2)

LASfile <- system.file("extdata", "Megaplot.laz", package="lidR")

las = readLAS(LASfile, select = "xyz")

p1 <- c(684800, y = 5017800)
p2 <- c(684900, y = 5017900)
tr <- clip_transect(las, p1, p2, width = 4, xz = T)

DSM <- tr@data[ , .(Z = max(Z)), by = list(X = plyr::round_any(X, 1))]

ggplot(tr@data) +
  aes(X,Z, color = Z) +
  geom_point(size = 0.5) + 
  geom_line(data = DSM, color = "black") +
  coord_equal() + 
  theme_minimal() +
  scale_color_gradientn(colours = height.colors(50))

^{Created on 2021-05-27 by the reprex package (v2.0.0)}