catalog_retile: Retile a LAScatalog

In lidR: Airborne LiDAR Data Manipulation and Visualization for Forestry Applications

Retile a LAScatalog

Description

Splits or merges files to reshape the original files collection (.las or .laz) into smaller or larger files. It also enables the addition or removal of a buffer around the tiles. Internally, the function reads and writes the chunks defined by the internal processing options of a LAScatalog. Thus, the function is flexible and enables the user to retile the dataset, retile while adding or removing a buffer (negative buffers are allowed), or optionally to compress the data by retiling without changing the pattern but by changing the format (las/laz). This function is does not load the point cloud into R memory It streams from input file(s) to output file(s) and can be applied to large point-cloud with low memory computer.

Note that this function is not actually very useful because lidR manages everything (clipping, processing, buffering, ...) internally using the proper options. Thus, retiling may be useful for working in other software, for example, but not in lidR

Usage

catalog_retile(ctg)

Arguments

ctg	A LAScatalog object

Value

A new LAScatalog object

Non-supported LAScatalog options

The option select is not supported and not respected because it always preserves the file format and all the attributes. select = "*" is imposed internally.

Examples

LASfile <- system.file("extdata", "Megaplot.laz", package="lidR")
ctg = readLAScatalog(LASfile)
plot(ctg)

# Create a new set of 200 x 200 m.las files with first returns only
opt_chunk_buffer(ctg) <- 0
opt_chunk_size(ctg) <- 200
opt_filter(ctg) <- "-keep_first"
opt_chunk_alignment(ctg) <- c(275, 90)
opt_output_files(ctg) <- paste0(tempdir(), "/retile_{XLEFT}_{YBOTTOM}")

# preview the chunk pattern
plot(ctg, chunk = TRUE)

newctg = catalog_retile(ctg)

plot(newctg)

# Create a new set of 200 x 200 m.las files
# but extended with a 50 m buffer in the folder

opt_chunk_buffer(ctg) <- 25
opt_chunk_size(ctg) <- 200
opt_filter(ctg) <- ""
opt_chunk_alignment(ctg) <- c(275, 90)
opt_output_files(ctg) <- paste0(tempdir(), "/{XLEFT}_{YBOTTOM}_buffered")
newctg = catalog_retile(ctg)

plot(newctg)


## Not run: 
# Create a new set of compressed .laz file equivalent to the original, keeping only
# first returns above 2 m

opt_chunk_buffer(ctg) <- 0
opt_chunk_size(ctg) <- 0
opt_laz_compression(ctg) <- TRUE
opt_filter(ctg) <- "-keep_first -drop_z_below 2"
opt_output_files(ctg) <- paste0(tempdir(), "/{ORIGINALFILENAME}_first_2m")
newctg = catalog_retile(ctg)

## End(Not run)

lidR documentation built on Sept. 11, 2024, 5:21 p.m.