## DESCRIPTION

v.in.lidar converts LiDAR point clouds in LAS format to a GRASS vector, using the libLAS library. The created vector is true 3D with x, y, z coordinates.

For larger datasets, it is recommended to not build topology (-b flag). Also, creating a table with attributes can take some time for larger datasets.

The optional spatial parameter defines spatial query extents. This parameter allows the user to restrict the region to a spatial subset while importing the data. All LiDAR points falling into this rectangle subregion are imported. The -r current region flag is identical, but uses the current region settings as the spatial bounds (see g.region).

A LiDAR pulse can have multiple returns. The first return values can be used to obtain a digital surface model (DSM) where e.g. canopy cover is represented. The last return values can be used to obtain a digital terrain model (DTM) where e.g. the forest floor instead of canopy cover is represented. The return_filter option allows selecting one of first, mid, or last returns.

LiDAR points can be already classified into standardized classes. For example, class number 2 represents ground (for other classes see LAS format specification in references). The class_filter option allows selecting one or more classes, as numbers (integers) separated by comma.

Note that proper filtering of the input points in not only critical for the analysis itself but it can also speed up the processing significantly.

### Decimation

Table with selected percentages of points to keep with corresponding decimation parameters:

percentage | parameters
--- | ---
0.1% | preserve=1000
1% | preserve=100
5% | preserve=20
10% | preserve=10
20% | preserve=5
25% | preserve=4
50% | skip=2
75% | skip=4
80% | skip=5
90% | skip=10

Table with selected fractions of points to keep with corresponding decimation parameters:

ratio | parameters
--- | ---
1/3 | preserve=3
1/4 | preserve=4
1/5 | preserve=5
1/6 | preserve=6

Table with selected fractions of points to throw away with corresponding decimation parameters:

ratio | parameters
--- | ---
1/3 | skip=3
1/4 | skip=4
1/5 | skip=5
1/6 | skip=6

## Project Creation

v.in.lidar attempts to preserve coordinate reference system (CRS) information when importing datasets if the source format includes such information, and if the LAS driver supports it. If the source dataset CRS does not match the CRS of the current project (previously called location) v.in.lidar will report an error message ("`Coordinate reference system of dataset does not appear to match current project`") and then report the PROJ_INFO parameters of the source dataset.

If the user wishes to ignore the difference between the coordinate system of the source data and the current project, they may pass the -o flag to override the CRS check.

If the user wishes to import the data with the full CRS definition, it is possible to have v.in.lidar automatically create a new project based on the CRS and extents of the file being read. This is accomplished by passing the name to be used for the new project via the project parameter. Upon completion of the command, a new project will have been created (with only a PERMANENT mapset), and the vector map will have been imported with the indicated output name into the PERMANENT mapset.

## NOTES

The typical file extensions for the LAS format are .las and .laz (compressed). The compressed LAS (.laz) format can be imported only if libLAS has been compiled with laszip support. It is also recommended to compile libLAS with GDAL, needed to test for matching CRSs.

## EXAMPLE

The sample LAS data are in the file "Serpent Mound Model LAS Data.laz", available at Serpent Mound Model LAS Data.laz

    # print LAS file info
    v.in.lidar -p input="Serpent Mound Model LAS Data.laz"

    # create a project with CRS information of the LAS data
    v.in.lidar -i input="Serpent Mound Model LAS Data.laz" project=Serpent_Mound

    # quit and restart GRASS in the newly created project "Serpent_Mound"
    # real import of LiDAR LAS data, without topology and without attribute table
    v.in.lidar -tb input="Serpent Mound Model LAS Data.laz" output=Serpent_Mound_Model_pts

## REFERENCES

ASPRS LAS format
LAS library
LAS library C API documentation

## SEE ALSO

r.in.lidar, r3.in.lidar, g.region, v.vect.stats, v.in.ogr

## AUTHORS

Markus Metz
Vaclav Petras, NCSU GeoForAll Lab (decimation, cats, areas, zrange)
based on v.in.ogr by various authors