Create a DTM using the TIN algorithm

Question

I am trying to create a DTM on a county wide level (so using LAS catalog). The lidRworkbook advises to use a buffer when using the TIN method, however the workbook doesn't show how to do that. So how can I first create this buffer? And how can I then use this buffer to create a dtm_tin?

On a side note is there a way to directly store the DTM raster to disk rather than first the rasterize_terrain tool first saves the DTM to memory (who knows I might run out of memory) and then save it using the raster or terra package?

Code:

# Create a LAS catalog
LAS_List = readLAScatalog("path", recursive = TRUE)

# Create a DTM using the TIN method
dtm_tin = rasterize_terrain(LAS_List, res = 1, algorithm = tin())

Answer 1

The way to work with a LAScatalog is explained in chap 14. The buffer is explained in section 14.7.2.

The default is 50 m buffer so your code is already correct.

To store the raster on disk see section 14.8.2. e.g

opt_output_files(LAS_list) <-  paste0("folder/{*}_dtm")

The path must be templated to generate one file per chunk. This is not explicitely mentionned in 14.8.2 but see help("LAScatalog-class")

Output options

The slot ⁠@output_options⁠ contains a list of options that determine how chunks (the sub-areas that are sequentially processed) are written. By "written" we mean written to files or written in R memory.

output_files: string. If output_files = "" outputs are returned in R. Otherwise, if output_files is a string the outputs will be written to files. This is useful if the output is too big to be returned in R. A path to a filename template without a file extension (the engine guesses it for you) is expected. When several files are going to be written a single string is provided with a template that is automatically filled. For example, the following file names are possible:

"/home/user/als/normalized/file_{ID}_segmented" "C:/user/document/als/zone52_{XLEFT}_{YBOTTOM}_confidential" "C:/user/document/als/{ORIGINALFILNAME}_normalized" This option will generate as many filenames as needed with custom names for each file. The allowed templates are {XLEFT}, {XRIGHT}, {YBOTTOM}, {YTOP}, {ID}, {XCENTER}, {YCENTER}, {ORIGNALFILENAME}. See opt_output_files.