Exporting crown boundaries from tree segmentation in R?

Question

I am using lidR package to segment my trees using lastrees directly from the points clouds.

The function works fine, however I would like to export to vector file the canopy boundaries from tree_segmentation that I did directly from my point cloud.

Is it possible to extract canopy boundaries from segmentation lastrees in order to analyze my results I got?

las = lastrees(lasn,li2012(R = 3, speed_up = 5))
plot(las, color = "treeID", colorPalette = col2)

Answer 1

This example is directly from the documentation @JRR provided. You can use writeOGR() from the rgdal package to write the convex hull polygons representing tree canopies to shapefile.

library(lidR)
library(rgdal)

las = readLAS("/path/to/your/points.las")
plot(las)

# Classify ground points
las = lasground(las, csf())
plot(las, color = "Classification")

# Normalize points
las = lasnormalize(las, tin())
plot(las)

# Calculate the canopy height model (CHM)
algo = pitfree(thresholds = c(0,10,20,30,40,50), subcircle = 0.2)
chm  = grid_canopy(las, 0.5, algo)
plot(chm, col = height.colors(50))

# Optionally smooth the CHM with a 3x3 pixel moving window with a median statistic
ker = matrix(1,3,3)
chm = focal(chm, w = ker, fun = median)
chm = focal(chm, w = ker, fun = median)

plot(chm, col = height.colors(50)) # check the image

algo = watershed(chm, th = 4)
las  = lastrees(las, algo)

# remove points that are not assigned to a tree
trees = lasfilter(las, !is.na(treeID))

plot(trees, color = "treeID", colorPalette = pastel.colors(100))

# Calculate tree metrics and convex hulls
metric = tree_metrics(las, .stdtreemetrics)
hulls  = tree_hulls(las)
hulls@data = dplyr::left_join(hulls@data, metric@data)

spplot(hulls, "Z")

# Write to shapefile
writeOGR(obj=hulls, dsn="/Users/aaron/Desktop/", layer="hulls", driver="ESRI Shapefile") # this is in equal area projection