Lidar – r.iresmi.net

Aiguille du Midi – CC-BY-SA by Ivan Borisov

Day 1 of 30DayMapChallenge: « Points » (previously).

IGN is scanning France using LIDAR. More than half the country is available for downloading currently. Let’s play with points around the Aiguille du Midi…

library(readr)
library(dplyr)
library(purrr)
library(fs)
library(lidR)

dir_create("tiles")

Selecting 4 squares on the selection map allows to generate a catalog of 1✕1 km tiles to download.

read_lines("liste_dalle.txt") |> 
  tibble(url = _) |> 
  mutate(file = path("tiles", path_file(url))) |> 
  pwalk(\(url, file) download.file(url, file))

Read and manipulate the LAZ files with the help of the {lidR} package. We only keep a region of interest 500 m around the peak.

ctg <- readLAScatalog("tiles")
roi <- clip_circle(ctg, x = 1001400, y = 6538400, radius = 500)

The point cloud has already been classified so we can extract only the ground (although at this altitude there is no vegetation).

ground <- filter_ground(roi)
plot(ground)

We display 38 millions points (50 points/m²)!

A 3d rendering of the Aiguille du Midi from LIDAR data — Figure 1: Aiguille du Midi in RGL

And then we can create a digital terrain model and a hillshade map…

dtm <- rasterize_terrain(roi, 2, tin(), pkg = "terra")
dtm_prod <- terra::terrain(dtm, v = c("slope", "aspect"), unit = "radians")
dtm_hillshade <- terra::shade(slope = dtm_prod$slope, aspect = dtm_prod$aspect)
plot(dtm_hillshade, col = gray(0:50/50), legend = FALSE)

A grayscale rendering of digital terrain model around Aiguille du Midi — Figure 2: DTM of Aiguille du Midi

--- title: "Lidar" description: "Day 1 of 30DayMapChallenge. Playing with points" author: "Michaël" date: "2024-11-01T16:00:00" date-modified: last-modified categories: - R - spatial - datavisualization - 30DayMapChallenge draft: false freeze: true editor_options: chunk_output_type: console chunk_output_type: console execute: eval: true --- ```{r} #| label: preview #| echo: false #| fig-cap: "Aiguille du Midi -- CC-BY-SA by Ivan Borisov" #| fig-alt: "Aiguille du Midi" #| fig-link: https://www.flickr.com/photos/borisov/11690877334/ #| class-output: "preview-image" #| out-width: "100%" knitr::include_graphics("images/11690877334_69272dd6b9_o.jpg") ``` Day 1 of [30DayMapChallenge](https://30daymapchallenge.com/): « Points » ([previously](/#category=30DayMapChallenge)). IGN is scanning France using [LIDAR](https://en.wikipedia.org/wiki/Lidar). More than half the country is [available](https://geoservices.ign.fr/lidarhd) for downloading currently. Let's play with points around the [Aiguille du Midi](https://en.wikipedia.org/wiki/Aiguille_du_Midi)... ```{r} #| label: config library(readr) library(dplyr) library(purrr) library(fs) library(lidR) dir_create("tiles") ``` Selecting 4 squares on the [selection map](https://diffusion-lidarhd.ign.fr/) allows to generate a catalog of 1✕1 km tiles to download. ```{r} #| label: download #| eval: false read_lines("liste_dalle.txt") |> tibble(url = _) |> mutate(file = path("tiles", path_file(url))) |> pwalk(\(url, file) download.file(url, file)) ``` Read and manipulate the LAZ files with the help of the [{lidR}](https://r-lidar.github.io/lidRbook/) package. We only keep a region of interest 500 m around the peak. ```{r} #| label: open_clip #| results: hide #| fig-show: hide ctg <- readLAScatalog("tiles") roi <- clip_circle(ctg, x = 1001400, y = 6538400, radius = 500) ``` The point cloud has already been classified so we can extract only the ground (although at this altitude there is no vegetation). ```{r} #| label: filter_visualize ground <- filter_ground(roi) plot(ground) ``` We display 38 millions points (50 points/m²)! ```{r} #| label: fig-rgl #| echo: false #| fig-cap: "Aiguille du Midi in RGL" #| fig-alt: "A 3d rendering of the Aiguille du Midi from LIDAR data" #| out-width: "100%" knitr::include_graphics("images/Capture d’écran du 2024-11-01 17-08-12.png") ``` And then we can create a digital terrain model and a hillshade map... ```{r} #| label: fig-rasterize #| results: hide #| fig-cap: "DTM of Aiguille du Midi" #| fig-alt: "A grayscale rendering of digital terrain model around Aiguille du Midi" #| out-width: "100%" dtm <- rasterize_terrain(roi, 2, tin(), pkg = "terra") dtm_prod <- terra::terrain(dtm, v = c("slope", "aspect"), unit = "radians") dtm_hillshade <- terra::shade(slope = dtm_prod$slope, aspect = dtm_prod$aspect) plot(dtm_hillshade, col = gray(0:50/50), legend = FALSE) ```