NAME

       v.lidar.correction   -  Corrects  the  v.lidar.growing output. It is the last of the three algorithms for
       LIDAR filtering.

KEYWORDS

       vector, LIDAR

SYNOPSIS

       v.lidar.correction
       v.lidar.correction --help
       v.lidar.correction  [-e]   input=name   output=name   terrain=name    [ew_step=float]     [ns_step=float]
       [lambda_c=float]   [tch=float]   [tcl=float]   [--overwrite]  [--help]  [--verbose]  [--quiet]  [--ui]

   Flags:
       -e
           Estimate point density and distance and quit
           Estimate  point  density  and  distance  in  map units for the input vector points within the current
           region extents and quit

       --overwrite
           Allow output files to overwrite existing files

       --help
           Print usage summary

       --verbose
           Verbose module output

       --quiet
           Quiet module output

       --ui
           Force launching GUI dialog

   Parameters:
       input=name [required]
           Name of input vector map
           Input observation vector map name (v.lidar.growing output)

       output=name [required]
           Output classified vector map name

       terrain=name [required]
           Name for output only ’terrain’ points vector map

       ew_step=float
           Length of each spline step in the east-west direction
           Default: 25 * east-west resolution

       ns_step=float
           Length of each spline step in the north-south direction
           Default: 25 * north-south resolution

       lambda_c=float
           Regularization weight in reclassification evaluation
           Default: 1

       tch=float
           High threshold for object to terrain reclassification
           Default: 2

       tcl=float
           Low threshold for terrain to object reclassification
           Default: 1

DESCRIPTION

       v.lidar.correction is the last of three steps to filter LiDAR data. The  filter  aims  to  recognize  and
       extract attached and detached object (such as buildings, bridges, power lines,  trees, etc.)  in order to
       create a Digital Terrain Model.
       The  module, which could be iterated several times, makes a comparison between the LiDAR observations and
       a bilinear spline interpolation with a Tychonov regularization parameter performed on the TERRAIN  SINGLE
       PULSE  points only. The gradient is minimized by the regularization parameter.  Analysis of the residuals
       between the observations and the interpolated values results in four cases (the  next  classification  is
       referred to that of the v.lidar.growing output vector):
       a) Points classified as TERRAIN differing more than a threshold value are interpreted and reclassified as
       OBJECT, for both single and double pulse points.
       b)  Points  classified  as  OBJECT  and  closed  enough  to  the interpolated surface are interpreted and
       reclassified as TERRAIN, for both single and double pulse points.

       The length (in mapping units) of each spline step is defined by ew_step for the east-west  direction  and
       ns_step for the north-south direction.

NOTES

       The input should be the output of v.lidar.growing module or the output of this v.lidar.correction itself.
       That  means,  this  module  could  be  applied more times (although, two are usually enough) for a better
       filter solution. The outputs are a vector map with a final point  classification  as  as  TERRAIN  SINGLE
       PULSE,  TERRAIN DOUBLE PULSE, OBJECT SINGLE PULSE or OBJECT DOUBLE PULSE; and an vector map with only the
       points classified as TERRAIN SINGLE PULSE or TERRAIN  DOUBLE  PULSE.   The  final  result  of  the  whole
       procedure  (v.lidar.edgedetection, v.lidar.growing, v.lidar.correction) will be a point classification in
       four categories:
       TERRAIN SINGLE PULSE (cat = 1, layer = 2)
       TERRAIN DOUBLE PULSE (cat = 2, layer = 2)
       OBJECT SINGLE PULSE (cat = 3, layer = 2)
       OBJECT DOUBLE PULSE (cat = 4, layer = 2)

EXAMPLES

   Basic correction procedure
       v.lidar.correction input=growing output=correction out_terrain=only_terrain

   Second correction procedure
       v.lidar.correction input=correction output=correction_bis terrain=only_terrain_bis

SEE ALSO

        v.lidar.edgedetection, v.lidar.growing, v.surf.bspline, v.surf.rst, v.in.lidar, v.in.ascii

AUTHORS

       Original version of program in GRASS 5.4:
       Maria Antonia Brovelli, Massimiliano Cannata, Ulisse Longoni and Mirko Reguzzoni
       Update for GRASS 6.X:
       Roberto Antolin and Gonzalo Moreno

REFERENCES

       Antolin,  R.  et  al.,  2006.  Digital  terrain  models  determination  by  LiDAR  technology:  Po  basin
       experimentation. Bolletino di Geodesia e Scienze Affini, anno LXV, n. 2, pp. 69-89.
       Brovelli  M. A., Cannata M., Longoni U.M., 2004. LIDAR Data Filtering and DTM Interpolation Within GRASS,
       Transactions in GIS, April 2004,  vol. 8, iss. 2, pp. 155-174(20), Blackwell Publishing Ltd.
       Brovelli M. A., Cannata M., 2004. Digital Terrain model reconstruction in urban areas from airborne laser
       scanning data: the method and an  example for Pavia (Northern Italy). Computers and Geosciences 30 (2004)
       pp.325-331
       Brovelli M. A. and Longoni U.M., 2003. Software per il filtraggio di dati LIDAR, Rivista dell’Agenzia del
       Territorio, n. 3-2003, pp. 11-22 (ISSN 1593-2192).
       Brovelli M. A., Cannata M. and Longoni U.M., 2002. DTM LIDAR in area urbana, Bollettino  SIFET  N.2,  pp.
       7-26.
       Performances  of the filter can be seen in the ISPRS WG III/3 Comparison of Filters report by Sithole, G.
       and Vosselman, G., 2003.

       Last changed: $Date: 2017-07-24 23:59:39 +0200 (Mon, 24 Jul 2017) $

SOURCE CODE

       Available at: v.lidar.correction source code (history)

       Main index | Vector index | Topics index | Keywords index | Graphical index | Full index

       © 2003-2018 GRASS Development Team, GRASS GIS 7.4.0 Reference Manual

GRASS 7.4.0                                                                           v.lidar.correction(1grass)