It is worth noting that systems of decidedly different reference
bases were tested. One system referred measurements only to
the track, while the other located them within a global system.
Both solutions have their flaws and advantages. Measurements
referred to tracks are less complicated, do not require
GNSS/IMU modules and yield higher clearance measurement
accuracy rates. Global measurements enable not only clearance
measurements but also examinations of some of track geometry
parameters (straight line sections, transition curves, circular
arcs, superelevations). The access to an absolute orientation is
at the expense of a slightly lower accuracy, which places itself
close to the acceptable limit, or exceeds it a little.
Figure 7. Clearance with measured railway infrastructure
elements obtained from rail gauge measurements,
at the background of the cloud of points from the
Z+F Profiler 9000 system
Figure 8. Clearance with measured railway infrastructure
elements obtained from rail gauge measurements,
at the background of the cloud of points originating
from the Riegl VMX - 250 system
4. DEVELOPMENT OF MEASUREMENT FLATCAR
MODEL PROTOTYPE
4.1 Conclusions from Field Measurements
Following the data analysis and examination of their quality, a
summary was prepared aiming at the indication of flaws and
advantages of particular systems. It was concluded that the best
solution would be a hybrid model, which combines both
solutions. In fact, System II could not cope well with recording
small elements, which means there were gaps in data covering,
e.g. roadside indicators. Here it seems to be appropriate to
reinforce the cloud of points with a third scanner, set
perpendicularly to the travelling direction.
In System I there was a quite high level of data noise. Without
support from the cloud of points from System I it was often
difficult to unambiguously identify objects.
International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Volume XXXIX-B4, 2012
XXII ISPRS Congress, 25 August — 01 September 2012, Melbourne, Australia
As regards image recording and arrangement of cameras, after
having analysed the recorded by Nikon cameras material, the
authors came to a conclusion that it was the forward view,
which was more useful than side view, and that conclusion
would be taken into account when developing the prototype.
4.0 Proposal of Measurement Flatcar Prototype
Conclusions drawn from field measurements and development
of a preliminary concept led to defining the measurement
system prototype model. It has been acknowledged that the
system should incorporate the following units:
- a scanner module,
- an image module,
- a GNSS/IMU recording module,
- a module for precision recording of rail heads.
The scanner module should include minimum three 2D
scanning lasers. Two pulse-type scanners may be set diagonally
and configured to perform measurements within the range of 1-
50 metres, with a minimum frequency of 100 Hz for each
scanner. The perpendicularly profiling scanner may be a phase
type of a frequency of 300 Hz. Presently, the maximum
profiling frequency for scanners available on the market is 200
Hz, therefore one may consider a temporary application of two
scanners. The system of scanners should provide a cloud of
points with the average distance between perpendicular profiles
of not more than 10 cm at the travelling speed of 100 km/h
(with the density of points in profile planes ranging from
several to a dozen or so millimetres). This will ensure detection
of elements in the clearance area and in its close surroundings
of the minimum dimensions of 10 x 10 cm. If two scanners are
applied, of profiling frequency of 200 Hz each, the resolution of
detail detection will increase, reaching the level of 7 cm in the
direction parallel to the track axis. There are no technological
barriers to increasing resolution in the perpendicular direction.
The laser scanners must be rigidly integrated with the
GNSS/IMU module. Another element is a set of 4-8 high
resolution photogrammetric cameras. Two pairs of cameras
constitute a set of photogrammetric cameras and are used for
performing additional, supplementary measurements.
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Figure 9. Model of measuring flatcar
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