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.
| 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 |
| ratio | parameters |
|---|---|
| 1/3 | preserve=3 |
| 1/4 | preserve=4 |
| 1/5 | preserve=5 |
| 1/6 | preserve=6 |
| ratio | parameters |
|---|---|
| 1/3 | skip=3 |
| 1/4 | skip=4 |
| 1/5 | skip=5 |
| 1/6 | skip=6 |
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.
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
Last changed: $Date$