NOTES
The
input in LIDAR data analisys
is the last pulse site list file.
The
edge detection procedure involves two different spline
interpolations: a bilinear one and a bicubic one with
different regularization weight values (lambda_g and lambda_r). [see
s.bspline.reg]
The gradient magnitude (G), derived from the bilinear spline surface,
the
bias value (S), between the bicubic spline surface and the raw data,
and the maximum slope
direction (D)
are
computed for every sites of the input.
Knowing that:
- an edge is characterized by a hight gradient magnitude, a
positive bias value and to belong to a chain element
- a point belongs to a chain element if its nearest points have
similar D values along the direction perpendicular to the maximum slope
direction
Taking into account a point P, being P1 and P2 the two nearest points
of P and D1
and D2 their maximum slope
direction, P
is classified as object if:
(i) G>Tg and
S>0
or
(ii)
G>tg, S>0,
(D-D1)<theta_g and
(D-D2) <theta_g and there is
almost one
point in the nearest eight<of P with
G>Tg
Every
point in the input site file is examinated and reclassified as:
·
Terrain (0)
·
Object (1)
·
Uncertain (2)
input format example (x|y|z):
513629.21|5403205.11|#0 %291.24
513629.25|5403206.53|#0 %291.28
513629.29|5403208.16|#0 %291.27
513629.33|5403209.69|#0 %291.29
513629.37|5403211.12|#0 %291.32
outClas format
example (x|y|z%classification%bicubic_interpolated_value):
499827.48|5418882.79|#0
%247.49 %0 %247.06513365
499827.1|5418870.68|#0 %246.7 %0 %246.32005415
499826.72|5418858.43|#0 %245.7 %1 %245.59059607
499826.33|5418846.07|#0 %244.65 %0 %244.9670436
499825.96|5418833.6|#0 %244.23 %2 %244.52604082
SEE ALSO
s.correction, s.bspline, s.growing, s.to.qrast
AUTHORS
Maria
A. Brovelli, Politecnico di Milano - Campus Como
Massimiliano Cannata, Politecnico
di Milano - Campus Como
Ulisse M.
Longoni, Politecnico
di Milano - Campus Como
REFERENCES
Brovelli M.A.;
Cannata M.; Longoni U.M., LIDAR Data Filtering and DTM Interpolation
Within GRASS
Transactions in GIS, April 2004, vol. 8, no. 2, pp.
155-174(20) - Blackwell Publishing Ltd
Pratt K
1991 Digital image processing (Second
edition). New York, NY, John Wiley and Sons