v.lidar.correction(1grass) GRASS GIS User's Manual v.lidar.correction(1grass)
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 vec-
tor 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 pa-
rameter. 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 ap-
plied more times (although, two are usually enough) for a better filter
solution. The outputs are a vector map with a final point classifica-
tion 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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