.TH v.lidar.correction 1grass "" "GRASS 7.8.5" "GRASS GIS User's Manual"
.SH NAME
\fI\fBv.lidar.correction\fR\fR  \- Corrects the v.lidar.growing output. It is the last of the three algorithms for LIDAR filtering.
.SH KEYWORDS
vector, LIDAR
.SH SYNOPSIS
\fBv.lidar.correction\fR
.br
\fBv.lidar.correction \-\-help\fR
.br
\fBv.lidar.correction\fR [\-\fBe\fR] \fBinput\fR=\fIname\fR \fBoutput\fR=\fIname\fR \fBterrain\fR=\fIname\fR  [\fBew_step\fR=\fIfloat\fR]   [\fBns_step\fR=\fIfloat\fR]   [\fBlambda_c\fR=\fIfloat\fR]   [\fBtch\fR=\fIfloat\fR]   [\fBtcl\fR=\fIfloat\fR]   [\-\-\fBoverwrite\fR]  [\-\-\fBhelp\fR]  [\-\-\fBverbose\fR]  [\-\-\fBquiet\fR]  [\-\-\fBui\fR]
.SS Flags:
.IP "\fB\-e\fR" 4m
.br
Estimate point density and distance and quit
.br
Estimate point density and distance in map units for the input vector points within the current region extents and quit
.IP "\fB\-\-overwrite\fR" 4m
.br
Allow output files to overwrite existing files
.IP "\fB\-\-help\fR" 4m
.br
Print usage summary
.IP "\fB\-\-verbose\fR" 4m
.br
Verbose module output
.IP "\fB\-\-quiet\fR" 4m
.br
Quiet module output
.IP "\fB\-\-ui\fR" 4m
.br
Force launching GUI dialog
.SS Parameters:
.IP "\fBinput\fR=\fIname\fR \fB[required]\fR" 4m
.br
Name of input vector map
.br
Input observation vector map name (v.lidar.growing output)
.IP "\fBoutput\fR=\fIname\fR \fB[required]\fR" 4m
.br
Output classified vector map name
.IP "\fBterrain\fR=\fIname\fR \fB[required]\fR" 4m
.br
Name for output only \(cqterrain\(cq points vector map
.IP "\fBew_step\fR=\fIfloat\fR" 4m
.br
Length of each spline step in the east\-west direction
.br
Default: 25 * east\-west resolution
.IP "\fBns_step\fR=\fIfloat\fR" 4m
.br
Length of each spline step in the north\-south direction
.br
Default: 25 * north\-south resolution
.IP "\fBlambda_c\fR=\fIfloat\fR" 4m
.br
Regularization weight in reclassification evaluation
.br
Default: \fI1\fR
.IP "\fBtch\fR=\fIfloat\fR" 4m
.br
High threshold for object to terrain reclassification
.br
Default: \fI2\fR
.IP "\fBtcl\fR=\fIfloat\fR" 4m
.br
Low threshold for terrain to object reclassification
.br
Default: \fI1\fR
.SH DESCRIPTION
\fIv.lidar.correction\fR 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.
.br
.br
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):
.br
.br
\fBa)\fR Points classified as TERRAIN differing more than a threshold
value are interpreted and reclassified as OBJECT, for both single and
double pulse points.
.br
.br
\fBb)\fR Points classified as OBJECT and closed enough to the
interpolated surface are interpreted and reclassified as TERRAIN, for
both single and double pulse points.
.PP
The length (in mapping units) of each spline step is defined by
\fBew_step\fR for the east\-west direction and \fBns_step\fR for the
north\-south direction.
.SH NOTES
The input should be the output of \fIv.lidar.growing\fR module or the
output of this \fIv.lidar.correction\fR 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 (\fIv.lidar.edgedetection\fR,
\fIv.lidar.growing\fR, \fIv.lidar.correction\fR) will be a point
classification in four categories:
.br
.br
TERRAIN SINGLE PULSE (cat = 1, layer = 2)
.br
TERRAIN DOUBLE PULSE (cat = 2, layer = 2)
.br
OBJECT SINGLE PULSE (cat = 3, layer = 2)
.br
OBJECT DOUBLE PULSE (cat = 4, layer = 2)
.SH EXAMPLES
.SS Basic correction procedure
.br
.nf
\fC
v.lidar.correction input=growing output=correction out_terrain=only_terrain
\fR
.fi
.SS Second correction procedure
.br
.nf
\fC
v.lidar.correction input=correction output=correction_bis terrain=only_terrain_bis
\fR
.fi
.SH SEE ALSO
\fI
v.lidar.edgedetection,
v.lidar.growing,
v.surf.bspline,
v.surf.rst,
v.in.lidar,
v.in.ascii
\fR
.SH AUTHORS
Original version of program in GRASS 5.4:
.br
Maria Antonia Brovelli, Massimiliano Cannata, Ulisse Longoni and Mirko Reguzzoni
.br
.br
Update for GRASS 6.X:
.br
Roberto Antolin and Gonzalo Moreno
.SH 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.
.br
.br
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.
.br
.br
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
.br
.br
Brovelli M. A. and Longoni U.M., 2003. Software per il filtraggio di dati
LIDAR, Rivista dell\(cqAgenzia del Territorio, n. 3\-2003, pp. 11\-22 (ISSN 1593\-2192).
.br
.br
Brovelli M. A., Cannata M. and Longoni U.M., 2002. DTM LIDAR in area urbana,
Bollettino SIFET N.2, pp. 7\-26.
.br
.br
Performances of the filter can be seen in the
ISPRS WG III/3 Comparison of Filters
report by Sithole, G. and Vosselman, G., 2003.
.SH SOURCE CODE
.PP
Available at: v.lidar.correction source code (history)
.PP
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.PP
© 2003\-2020
GRASS Development Team,
GRASS GIS 7.8.5 Reference Manual