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Test facility on positioning systems (SESSYL)
A mobile rail-mounted carriage fitted with a three-axis
platform follows a reference path that serves as the basis
for comparing the path provided by the tested positioning
system. This carriage and the test track together constitute
"Sessyl", the positioning system evaluation
facility set up at the LCPC Nantes Center between 1994
and 1995. Special software then enables processing the
data recorded during testing and generates a report on
the results obtained. Intended specifically for civil
engineering applications, the studies conducted using
Sessyl have given rise to a wide array of partnerships,
primarily with firms working in the field of GPS, such
as Trimble, Thalès Navigation, Leica Geosystems,
Novatel, Navstar, Geotronics, but also with the manufacturers
of positioning equipment that utilize optics technologies
(Leica, Zeiss) or inertial technologies (KVH), etc. Moreover,
Sessyl has provided the opportunity to enter into partnerships
with institutions and universities (e.g. SNCF, DGA, the
European project CIRC, University of Newcastle, Ecole
Centrale de Nantes, University of London).
This testing facility is truly one of a kind, whether
at the European scale or worldwide.
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· Unit assigned responsibility for equipment operations:
Division for Sustainable Approaches in Civil Engineering (DDGC)
· Sectors of activity:
- Roads
- Earthwork
- Civil engineering
structures
Contact:
Division
for Sustainable Approaches in Civil Engineering
(DDGC)
An exemplary application:
Precision GPS applied to the real-time positioning of vehicles
Within the scope of a research project focusing
on the real-time positioning and automation of road
construction vehicles, the LCPC conducted in 1996
a study in order to better ascertain the level of
vertical precision that a GPS "real-time kinematic"
(RTK) receiver is actually capable of attaining
under work site use conditions.
The "SESSYL" test bench has been heavily
involved for the purposes of this study, due to
its design for high-precision, real-time evaluation
testing of positioning systems. The study has been
carried out by LCPC with the cooperation and backing
of the French road-building company COLAS and the
ESGT School of Land Surveying and Topography.
An appropriate geodesic transformation procedure,
compatible with the set of precision-related specifications,
was initially proposed. Next, the main results stemming
from a special test program were discussed as part
of an in-depth examination of the impact of certain
parameters on vertical GPS precision.
The central section of the study dealt with an analysis
of the standard sequence of GPS RTK positions, which
then served as a basis for identifying key characteristics,
i.e.: high-frequency noise (relatively simple to
filter) and low-frequency bias. Given its undoubted
repeatability, this bias may be modeled and predicted,
thereby making it possible to improve real-time
positioning precision.
As a means of validating the study on a full-size
model, an experimental work site was used in order
to introduce a typical piece of road-building equipment
(a pavement finisher), operated under actual use
conditions.
Finisher fitted with a GPS and the experimental
work site
used for validation purposes near Orleans
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·
Technical characteristics:
The Sessyl operating principle consists of having
the tested system follow a programmable and perfectly-known
vehicle path. For this purpose, the system is placed
on a metallic rail-mounted carriage equipped with
a motorized three-axis platform. The comparison
between the actual path followed and that measured
by the system provides considerable information
on system quality.
Estimated precision (± 2 standard
deviation):
| Speed |
Axially |
Laterally |
Vertically |
Loop |
Roll |
Pitch |
| 0.35 km/h |
± 10 mm |
± 2 mm |
± 2 mm |
± 0.1° |
± 0.05° |
± 0.05° |
| 1 km/h |
± 10 mm |
± 2.5 mm |
± 2 mm |
± 0.1° |
± 0.07° |
± 0.07° |
| 5 km/h |
± 10 mm |
± 3 mm
(straight sections)
± 5 mm (curves)
|
± 2 mm |
± 0.1° |
± 0.1°
(straight sections)
± 0.2° (curves)
|
± 0.1° |
| 15 km/h |
± 10 mm |
± 5 mm
(straight sections)
± 10 mm (curves)
|
± 2 mm |
± 0.1° |
± 0.2°
(straight sections)
± 0.4° (curves)
|
± 0.1° |
Rail geometry
CHARACTERISTICS:
Size
of carriage dismounted: 3 m x 1 m x
1 m
Mass of the carriage: 450 kg
Mountable mass: 15
kg maximum |
Cross-section
of the rail-mounted carriage |
| Motion |
Max
speed |
| Vertical |
Total motion
(300 mm) in 2 s |
| Roll |
Total motion
(-6 à +6°) in 2 s |
| Pitch |
Total motion
(-6 à +6°) in 2 s |
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| Range |
Min. speed |
Max. speed |
| Slow |
0.05 km/h |
1 km/h |
| Fast |
1 km/h |
15 km/h |
· Operational since: set up in 1994, first tests conducted in 1995.
· Application examples:
1995: Comparison of 3 types of GPS RTK receivers
1996: Study of GPS-guided paving machines
1997:
- joint study with
the SNCF Railway on GPS-assisted thickness measurements
- collaborative research
efforts with the University of Newcastle and LRBA
- comparison of 5
GPS RTK receivers for CIRC
1998:
- testing on DGPS
equipment for the road survey vehicles of the Ponts
et Chaussées network
- first test conducted
on a combined GPS-GLONASS receiver
1999:
- first test of a
robotic total station (Leica)
- joint research program
with ETAS on test operating methods
- first test conducted
on an inertial measurement unit with ETAS
- evaluation of the
LaserGuide sensor developed by a CIRC partner
- testing of a new
GPS RTK receiver
2000:
- testing on LaserGuide,
in a coordinated effort with both IRCCyN
(Ecole Centrale de Nantes) and the University of
East London
- feasibility
testing with 3 types of centimetric GPS equipment
used in postprocessing for research on the GPS precise
road leveling
2001:
- testing of a GPS
RTK device for EDF (electrical utility)
- 2 testing campaigns
on a GPS compass for Thalès Navigation
- testing of an inertial
measurement unit for LIVIC
- tests conducted
on hardware and software configurations for LRBA
(DGA)
- testing of 2 combined
GPS-inertia units for Sirehna
- used as part of
the acceptance testing procedure for the LocAGR
prototype
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