## 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

## Location Creation

v.in.lidar attempts to preserve projection information when importing datasets if the source format includes projection information, and if the LAS driver supports it. If the projection of the source dataset does not match the projection of the current location v.in.lidar will report an error message ("`Projection of dataset does not appear to match current location`") and then report the PROJ_INFO parameters of the source dataset.

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

If the user wishes to import the data with the full projection definition, it is possible to have v.in.lidar automatically create a new location based on the projection and extents of the file being read. This is accomplished by passing the name to be used for the new location via the location parameter. Upon completion of the command, a new location 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 projections.

## EXAMPLE

This example is analogous to the example used in the GRASS wiki page for importing LAS as vector points.

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

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

      # create location with projection information of the LAS data
      v.in.lidar -i input="Serpent Mound Model LAS Data.las" location=Serpent_Mound

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

## SEE ALSO

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

## REFERENCES

ASPRS LAS format
LAS library
LAS library C API documentation

## AUTHOR

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

Last changed: $Date$