LIDAR

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LIDAR and Multi-beam Swath bathymetry data

Modules

Import

  • r.in.xyz - Create a raster map from an assemblage of many coordinates using univariate statistics.
    (example)
  • v.in.ascii - Import data from an ASCII file to GRASS vector format.
    Limited to a few million data points unless topology and database creation is skipped with the -bt flags

Analysis

  • v.outlier - Removes outliers from vector point data.
  • v.lidar.growing - Building contour determination and Region Growing algorithm for determining the building inside.
  • v.lidar.correction - Correction of the v.lidar.growing output. It is the last of the three algorithms for LIDAR filtering.

Surface generation

  • v.surf.rst - Spatial approximation and topographic analysis using regularized spline with tension.
  • v.surf.idw - Surface interpolation from vector point data by Inverse Distance Squared Weighting.
  • v.surf.bspline - Surface interpolation from vector point data by bicubic or bilineal interpolation with Tykhonov regularization.
  • r.fillnulls - Fills no-data areas in raster maps using v.surf.rst splines interpolation.

Swath Bathymetry Tools

see also the Marine_Science#Multibeam_sonar_processing wiki page

  • The v.swathwidith module by David Finlayson for planning surveys. (development page)
  • GRASS integration with MB-System (GPL) software for processing Multibeam and Sidescan Sonar data. GRASS + MBsys + GMT make a nice scriptable trio.

LIDAR Tools

  • r.terraflow - computation of flow direction, flow accumulation and other basic topographic terrain indices from massive raster digital elevation models (DEM). From the Duke University STREAM project.
  • LAStools are a set of simple command line tools (including source code) for converting to/from ASCII, viewing, comparing, and compressing LIDAR data.
  • libLAS ASPRS LiDAR data translation tools

Examples

Check bounds and SRS:

lasinfo "Serpent_Mound_Model_LAS_Data.las"
[...]
 Min X Y Z                  289020.900000 4320942.610000 166.780000
 Max X Y Z                  290106.020000 4323641.570000 215.480000
Spatial Reference           +proj=utm +zone=17 +ellps=WGS84 +units=m 


After creating a suitable UTM zone 17 location (EPSG:32617) set the region according to the information from lasinfo at 1m resolution, rounding grid outwards to align to whole meters:

g.region n=4323641.57 s=4320942.61 w=289020.90 e=290106.02 res=1 -ap


Finally, import with r.in.xyz with data piped directly from the las2txt program and set a nice equalized color table:

las2txt --stdout "Serpent_Mound_Model_LAS_Data.las" | \
   r.in.xyz in=- out=Serpent_Mound_Model_LAS_Data fs=space
r.colors Serpent_Mound_Model_LAS_Data color=bcyr -e

Clean DEM:

# convert to vector points
r.to.vect -z feature=point in=Serpent_Mound_Model_LAS_Data out=Serpent_Mound_Model_LAS_pt

# interpolate using a regularized spline fit
v.surf.rst layer=0 in=Serpent_Mound_Model_LAS_pt elev=Serpent_Mound_Model_LAS.rst

# create buffer area around origial data points
r.buffer in=Serpent_Mound_Model_LAS_Data out=Serpent_Mound_Model_LAS.5m_buff dist=5

# crop interpolated DEM to only include areas nearby actual data
r.mapcalc 'Serpent_Mound_Model_LAS.smooth = \
  if(isnull(Serpent_Mound_Model_LAS.5m_buff), \
     null(), Serpent_Mound_Model_LAS.rst'

# set colors to something nice
r.colors Serpent_Mound_Model_LAS.smooth color=bcyr -e

Sample data

Widely used in GRASS tutorials

Other

  • USGS Center for LIDAR Information Coordination and Knowledge (aka CLICK) - USGS LiDAR point cloud distribution site
    http://lidar.cr.usgs.gov
  • EarthScope Spatial Data Explorer - A java application for querying, browsing, and acquiring data from the EarthScope Spatial Data Repository. Currently includes a number of LiDAR datasets.
    http://www.earthscope.org/data/lidar.php

Links

  • libLAS - LAS 1.0/1.1 ASPRS LiDAR data translation toolset