ALS-data-preprocessing.md

+This workflow proposes `R` functions for checking and preprocessing Airborne Laser Scanning (lidar remote sensing) data. It is based on functions from R package `lidR`, and it includes the following steps:
++ check the content of one file, 
++ create images and statistics from multiple files,
++ compute digital surface models.
+
+The following files are provided:
+* [Rmarkdown source](https://gitlab.irstea.fr/jean-matthieu.monnet/lidartree_tutorials/-/blob/master/R/ALS_data_preprocessing.Rmd),
+* [**ALS data preprocessing tutorial in html**](https://gitlab.irstea.fr/jean-matthieu.monnet/lidartree_tutorials/-/raw/master/export/ALS_data_preprocessing.html?inline=false),
+* [ALS data preprocessing tutorial in pdf](https://gitlab.irstea.fr/jean-matthieu.monnet/lidartree_tutorials/-/blob/master/export/ALS_data_preprocessing.pdf),
+* a [bibliography file](https://gitlab.irstea.fr/jean-matthieu.monnet/lidartree_tutorials/-/blob/master/bib/bibliography.bib)
+* datasets required to run the source code are also available on the repository.
+
+
+Changelog
+* Sept. 21, 2021: first release
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