readLAS: Read .las or .laz files

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

Read .las or .laz files

Description

Reads .las or .laz files into an object of class LAS. If several files are read at once the returned LAS object is considered as one LAS file. The optional parameters enable the user to save a substantial amount of memory by choosing to load only the attributes or points of interest. LAS formats 1.0 to 1.4 are supported. Point Data Record Format 0 to 10 are supported.

readLAS is the original function and always works. Using one of the read*LAS functions adds information to the returned object to register a point-cloud type. Registering the correct point type may improve the performance of some functions by enabling users to select an appropriate spatial index. See spatial indexing. Notice that by legacy and for backwards-compatibility reasons, readLAS() and readALSLAS() are equivalent because lidR was originally designed for ALS and thus the original function readLAS() was (supposedly) used for ALS. Reading a TLS dataset with readLAS() instead of readTLSLAS() is perfectly valid and performs similarly to versions ⁠<= 3.0.0⁠, with neither performance degradation nor improvements.

Usage

readLAS(files, select = "*", filter = "")

readALSLAS(files, select = "*", filter = "")

readTLSLAS(files, select = "*", filter = "")

readUAVLAS(files, select = "*", filter = "")

readDAPLAS(files, select = "*", filter = "")

readMSLAS(files1, files2, files3, select = "*", filter = "")

Arguments

files	characters. Path(s) to one or several a file(s). Can also be a LAScatalog object.
select	character. Read only attributes of interest to save memory (see details).
filter	character. Read only points of interest to save memory (see details).
files1, files2, files3	characters. Path(s) to one or several a file(s). Each argument being one channel (see section 'Multispectral data'). 'files2' and 'files3' can be missing.

Details

Select: the 'select' argument specifies the data that will actually be loaded. For example, 'xyzia' means that the x, y, and z coordinates, the intensity and the scan angle will be loaded. The supported entries are t - gpstime, a - scan angle, i - intensity, n - number of returns, r - return number, c - classification, s - synthetic flag, k - keypoint flag, w - withheld flag, o - overlap flag (format 6+), u - user data, p - point source ID, e - edge of flight line flag, d - direction of scan flag, R - red channel of RGB color, G - green channel of RGB color, B - blue channel of RGB color, N - near-infrared channel, C - scanner channel (format 6+), W - Full waveform. Also numbers from 1 to 9 for the extra bytes data numbers 1 to 9. 0 enables all extra bytes to be loaded and '*' is the wildcard that enables everything to be loaded from the LAS file.
Note that x, y, z are implicit and always loaded. 'xyzia' is equivalent to 'ia'.

Filter: the 'filter' argument allows filtering of the point cloud while reading files. This is much more efficient than filter_poi in many ways. If the desired filters are known before reading the file, the internal filters should always be preferred. The available filters are those from LASlib and can be found by running the following command: readLAS(filter = "-help"). (see also rlas::read.las). From rlas v1.3.6 the transformation commands can also be passed via the argument filter.

Value

A LAS object

Full waveform

With most recent versions of the rlas package, full waveform (FWF) can be read and lidR provides some compatible functions. However, the support of FWF is still a work-in-progress in the rlas package. How it is read, interpreted and represented in R may change. Consequently, tools provided by lidR may also change until the support of FWF becomes mature and stable in rlas. See also rlas::read.las.

Remember that FWF represents an insanely huge amount of data. It terms of memory it is like having between 10 to 100 times more points. Consequently, loading FWF data in R should be restricted to relatively small point clouds.

Multispectral data

Multispectral laser data are often stored in 3 different files. If this is the case readMSLAS reads the .las or .laz files of each channel and merges them into an object of class LAS and takes care of attributing an ID to each channel. If the multisprectral point cloud is already stored in a single file leave file2 and file3 missing.

Examples

LASfile <- system.file("extdata", "Megaplot.laz", package="lidR")
las = readLAS(LASfile)
las = readLAS(LASfile, select = "xyz")
las = readLAS(LASfile, select = "xyzi", filter = "-keep_first")
las = readLAS(LASfile, select = "xyziar", filter = "-keep_first -drop_z_below 0")

# Negation of attributes is also possible (all except intensity and angle)
las = readLAS(LASfile, select = "* -i -a")

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