Adding segments3d to a view 3D from lidr

Question

I want to add segments represent the tree of apex tree, how to add segments3d to the plot below ?

library(lidR)
library(rgl)

LASfile <- system.file("extdata", "MixedConifer.laz", package="lidR")
las <- readLAS(LASfile, select = "xyz", filter = "-drop_z_below 0")

ttops <- tree_detection(las, lmf(ws = 5))

plot(las) %>%
  add_treetops3d(ttops) %>%
  segments3d(...)

What are arguments of ... ?

Answer 1

The key point here is that the point cloud is not rendered with actual XY coordinates because rgl is working with float instead of double and this create artifacts when displaying the point cloud. The coordinates are thus shifted to get a nice rendering.

To display your segments you must shift their coordinates as well. plot returns the offset values applied. In the following example I assumed that you wanted to plot the trunks of the trees

library(lidR)
library(rgl)

LASfile <- system.file("extdata", "MixedConifer.laz", package="lidR")
las <- readLAS(LASfile, select = "xyz", filter = "-drop_z_below 0")

ttops <- tree_detection(las, lmf(ws = 5))

x = coordinates(ttops)[,1]
y = coordinates(ttops)[,2]
z = ttops$Z

offset = plot(las)
add_treetops3d(offset, ttops)

xoffset = offset[1]
yoffset = offset[2]

for (i in 1:length(ttops))  
{
  X = c(x[i], x[i]) - xoffset
  Y = c(y[i], y[i]) - yoffset
  Z = c(0, z[i])
  segments3d(X, Y, Z, col = "white", size = 2)
}