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.

SOURCE CODE

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

       Accessed: unknown

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