The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences. Vol. XXXVII. Part B5. Beijing 2008
603
5. EXPERIMENTAL RESULTS
There is no need to search rotation matrix values for
a ll R e 50(3) area in laser scanning practice. Most of laser
3x3
scanners have a compensatory mechanism which guarantees the
parallelism of Z axis for all scans. Therefore, we have found
the correlation function considering rotation of the coordinate
system of the second scan around Z axis only by angle
k e (-180°, 180°) with step of 3°. The pre-alignment results
using orientation histograms are presented on figure 2(B). The
size of V is limited to 75x75x75 voxels. The size of each scan
is about 500 000 points.
6. CONCLUSIONS
We have presented the fully automated pre-alignment algorithm
using orientation histograms. The accurate solution of the whole
problem can be found after applying ICP based algorithm using
founded initial estimations. Presented algorithm is effective
even with large initial angles (> 100°) between registered point
clouds. This algorithm is simple in the implementation. The
practical tests show robust and reliable results.
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APPENDIX A
Lets y and y be the binary voxel presentations of scans
MxNxK MxNxK
P x (Xj ,y x ,z 1) and P 2 (jc 2 ,y 2 ,z 2 ) respectively with the same
angular orientation. Lets
P x = P 2 + AT ,
(5)
where
AT =
, is a vector that corresponds to the maximum
of correlation function (4).
Adds additional zero values to y and y :
MxNxK MxNxK
and
K
= [V 0
K
v 0 ]
(3M-2)x(3N-2)x(3K-2)
MxNxK
V 2
= [
K0
V 0 ]
3M-2)x(3N-2)x(3K-2)
MxNxK
(6)
where V n = 0 •
M-\xN-\xK-\
Values of corresponding normalized correlation function G can
be calculated using (8):
G =
> < 8 >
2M IN 2K M N K
, ittwj.u-tttwj,*)-
\ I M j=N l=K i=1 7=1 /=1
where
Jft () - discrete forward Fourier transform on R3,
ifft () - discrete inverse Fourier transform on R3,
COnj () - function for calculation of complex conjugating
elements of matrix.
Accordingly,
'i 0m -M-2'
min(x,) N
min(x 2 )^
A T =
jc„-N-2
■S v +
min(y,)
-
min(y 2 )
min(z,)^
,min(z 2 ) y
where
(i n , / ~ ,k r )-indices of the maximal element of G,
V G^ Omax ’ ^max '
S v - the size of the voxel side.