v.lidar.correctiongrass - Online in the Cloud

PROGRAM:

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
Estimate point density and distance for the input vector points within the current
region extends 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]
Only ’terrain’ points output vector map

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

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

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.

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

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