before the matching. In term of phase space, the scan
is positioned close to a saddle point. Due to this, in
term of probability, we favor in the first iteration one
side of the pipeline more than the other. In addition,
the barrier between the two regions of the pipeline
should be high. This implies that even with our
metropolis criteria, passing the barrier is difficult.
However, we treat a realistic industrial object, and we
can assure correct matching if we keep only the best
matching over the 200 tests. We already have leads to
get performance improvement like taking the initial
position and orientation of the scan into account
thanks to IMU information. For the lego, we see it is
a difficult case for matching. This is mainly due to the
size and the point density of the scan. It implies less
constrain compared to the pipeline and so, more local
minima.
In term of computational time, our method is
efficient. The complete matching algorithm took
between 10 and 20 seconds for all the tested case. Our
method is faster than Go-ICP. Half of the
computational time is due to the point cloud pre-
processing. For difficult cases, Go-ICP
computational time can explode (~ 1 hour).
Finally, concerning the fitness and the RMSE,
these two values are good performance criteria that
can be used to interpret the matching quality. For
most of the cases, a fitness value over 80% and with
a RMSE below the millimeter means we have a good
matching. In the case where Go-ICP shows good
results, the method has a lower RMSE value and
wider fitness value. Nevertheless, the adaptability
showed by our approach is interesting for inspection
application where objects are complex.
5 CONCLUSIONS
In this work, we proposed a MCMH approach
combined with ICP for the point cloud matching
problem. We showed encouraging results compared
to a state-of-the-art method called Go-ICP. Our
method includes a 3D reconstruction step using ICP
color generating 3D models to compare scans. The
method is efficient on small objects like the lego, and
seems adapted to realistic objects for inspection
problem like the pipeline system.
Our approach still suffers from some limitations,
especially in difficult cases where there is some
symmetry in the object of interest. The simplified
triangular mesh descriptor we used could be too
restrictive for such case, causing some trouble for
matching. Some improvement can be done by
changing the initial position of the scan for the
matching. Parallelization of MCMH can also
conserve efficient results while reducing the actual
computation time of less than 20 seconds, which can
let us consider a quasi-real-time application.
In the future, we plan to use this approach to
perform geometrical comparison between a scan and
its reference model, to highlight the presence of
defects using similarity criterion. Highlighted region
of interest will reveal the presence of defects like
missing pieces, extra pieces or misoriented pieces.
This method could then be used for detection of
foreign objects in aeronautical assembly lines or
missing pieces for maintenance for example. Further
tests on realistic industrial environment, with
different object sizes and complexity, are also
planned to validate the method usability. A last
improvement for this method could be to simulate a
video processing approach through the fusion of
several partial scans to inspect before comparing with
the 3D model. It could improve robustness by adding
more information and increasing artificially the
sensor precision.
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