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  • AS-BULIT SURVEY AND 3D MODELING OF HIGHWAYS IN GREECE
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MAJOR INFRASTRUCTURES

Road intersections survey and modeling for the design and evaluation of safety improvement measures at high risk locations all over Greece

Purpose
The project was assigned by the Maintenance Department of the Greek Ministry of Infrastructures, Transports and Networks in order to improve safety for high accident risk locations (mainly road junctions) all over the Greek road network and, in particular, to design and evaluate through video simulations the appropriate improvement interventions for these locations.

 

 

Project tasks
• Selection of “high accident occurrence - reduced safety” locations by the Maintenance Department.
• Laser scanning survey, using the Optech ILRIS 36D Laser Scanner, of the road intersection area for each location.   Sufficient road length had to be covered in order to create driving video simulations, at least 200 – 300 m for each intersecting   road. Required resolution was about 5-10 cm, with an accuracy of 5 cm. Scanner was placed on the roof of a vehicle or lifted by   a lifting device. Approximately 10 scanning positions were required per location, with a distance between scans 50 – 80 m and   20% (maximum) pan-tilt base overlap was used.
• Alignment and georeference of the pointclouds to create a single colored and georeferenced point cloud for the surveyed area.   Georeference was performed using the scanning stations as well as conical targets, surveyed with GPS from state geodetic   control points.
• Vector drawings (feature collection) and orthophotos (directly from colored scanned points) were created as a background for   design purposes.
• Design of safety improvement interventions: additional lanes (including acceleration – deceleration lanes), vertical and horizontal   signage, changes in traffic regulation, closure of secondary roads, etc. Design was performed in vector format and new road   elements were modeled in 3D (as polygonal models).
• Vertical signage modeling (necessary for proper display of traffic signs in 3D video simulations) was performed by creating a   small VRML model for each traffic sign. Traffic sign pictures were overlaid on circular, triangular, etc, 3D surfaces and exported   as VRML models. Standard traffic sign pictures were available, while digital pictures of non-standard signs (e.g. showing   directions) were taken and photos were ortho-rectified based on the shape of the sign. Finally, new (according to the design)   signage pictures were created using image processing software.
• Editing – cleaning of the initial pointcloud was performed and polygonal models of new road elements, as well as signage VRML   models, were imported in a single environment, to create the “as designed” total 3D model.
• Video fly - through and driving simulations were created. Driving simulations (from all possible origins to all possible destinations)   were generated by applying vehicle trajectories and calculating distances and video frame intervals to simulate movement with   variable speed. The same video frame sequences were applied to “before” and “after” models to create comparative results.
• Video simulations were evaluated by the staff of the Maintenance Department and the Local Authorities in order to approve the   designed measures for construction or forward the design for further revision and improvement.


 

 

Results - Conclusions
Laser scanning has proven to be not only a fast data capture tool to provide accurate and complete survey background data for road design purposes, but also an easy and efficient way of creating “before / existing” and “after / as designed” colored video fly- through and driving simulations to easily compare and evaluate the efficiency of designed – proposed interventions, before their actual implementation.

 

 

Related Videos
http://www.youtube.com/watch?v=FyLVfperBX0
http://www.youtube.com/watch?v=4oioI2bEfxg
http://www.youtube.com/watch?v=qyEAwWtgYVg
http://www.youtube.com/watch?v=OO_-NdHSXRE
http://www.youtube.com/watch?v=wEG8sHlpAH0
http://www.youtube.com/watch?v=-eoPUNOvXQ4
http://www.youtube.com/watch?v=4M_uMQwdsaY
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As-built survey and 3D modeling of Highways in Greece:
• Korinthos - Tripoli highway (static TLS)
• Elefsina - Korinthos highway (mobile TLS)

Purpose
Concession Self Financing Projects have been, during the last decade, a common practice for the construction of road transport networks. The basic concept is that a large private J/V undertakes the construction of a new highway section and in the same time takes the responsibility for the maintenance (and improvement) of an existing highway section, from which it collects the toll fees, in order to finance the whole project. After completing the project, the J/V has its full exploitation for a certain number of years, according to the concession contract.
An obvious need for detail surveys of the existing highway sections arises from the whole process.
These surveys usually require:
• Detail “as-built” survey of all highway features (pavement, structures, slopes, signage, poles, etc).
• Efficient archiving of “as-built” situation for future reference.
• Positional accuracy: 2-3 cm.
• Elevation accuracy: 1-2 cm.
• 3D model (TIN) for highway reconstruction design.
• Background survey maps (scale 1:500).
• No significant traffic closure or delay.
• Efficient safety plan.
• Permits from local traffic authorities.

 

Applying TLS methodology
Terrestrial Laser Scanning techniques have been applied in two cases of existing highways (dual carriageway, 2-3 lanes & shoulder), using two different approaches:
• Korinthos – Tripoli highway (length 80 km, J/V MOREAS) was surveyed in 2006-2007 using a static (scan & go) approach with an Optech ILRIS 36D Laser Scanner.
• Elefsina – Korinthos highway (length 60 km, J/V APION KLEOS) was surveyed in 2008 using a mobile approach with the newest Optech LYNX Mobile Mapper.

 

Project Tasks
a. Korinthos - Tripoli: Field work tasks and parameters

• Establishment of geodetic infrastructure networks (triangulation, leveling, polygonometry), also necessary for construction.
• Static (stop & scan) laser scanning with Optech ILRIS36D.
• Scanner carried by a vehicle moving or standing always on the shoulder lane, protected by a traffic regulation trailing vehicle.
• Scanning from both sides of the highway, distance between scanning positions 50-80m.
• 1100 total scanning stations, 120 working days for 80 km of highway.

• Critical issue for horizontal objects: lifting the scanner (better scanning angle, improved object visibility, lower scanning resolution   and / or fewer scanning positions required).
• Lifting device used: Genie Super Hoist (5.6m, 113 kg capacity, CO2).
• Custom modifications: Trailer integration, 5/8 bolt, longer ethernet and power cables, stabilizers, fuel generator & UPS, et
• Scanning resolution: 55mm @ 25m horizontal / 20mm @ 25m vertical.
• Pan-tilt base overlap set to maximum (20% overlap, 15 frames/3600).
• Primary georeferencing: with conic targets (standard traffic cones: easy to install, measure and model), 1 cone (anchor point)   per scan position required for sequential georeferencing.

b. Elefsina - Korinthos: Field work tasks and parameters
• Establishment of geodetic infrastructure networks (triangulation, leveling, polygonometry), also necessary for construction.
• Mobile laser scanning with Optech LYNX Mobile Mapper (collaboration with SINECO).
• Sensors – GPS/IMU carried by a vehicle moving at 50 km/h on the shoulder and left lane, protected by traffic regulation vehicles.
• 2 passes for each carriageway (shoulder lane – left lane) for better data quality.
• 240 km total scanning distance, 1 working day for 60 km of highway.
• Base GPS station support (6 base stations on known points).
• Measurement of positional Ground Control Points (natural targets identifiable on pointcloud).

 

• Basic data processing / alignment and delivery of georeferenced pointclouds in 500 m segments for each carriageway.
• Conversions between global (WGS84/UTM/zone 34) and local (CGRS87) geodetic reference systems.
• Positional GCP alignment for groups of 3-5 segments of 500 m (typical target registration accuracy < 3cm).

c. Common post-processing tasks
• Georeferencing refinement for elevations: using additional points measured on both edges of each carriageway every 50-80m   (typical elevation alignment accuracy < 1 cm).
• Feature collection from pointclouds.
• 3D Modeling (TIN) from features and Survey Maps (scale 1:500) generation.
• Archiving for future reference: Pointclouds segmented per km.

Results - Conclusions
While the newest mobile TLS approach using the LYNX Mobile Mapper is obviously the method of choice, the static approach with the ILRIS still has some advantages and can be applied at least for smaller road sections, taking into account also the cost of the two systems. The comparison conclusions between the two methods, in terms of data quality, accuracy and productivity are presented below:

 

Data Quality

LYNX:
• Uniform resolution homogeneous pointclouds.
• No unnecessary overlaps.
• Less noise from passing traffic.
• Better object coverage with 2 sensors.

ILRIS:
• Better detail for close objects.
• Better viewing angle when lifted.
• Produces organized pointclouds (with normal vectors).

Accuracy

LYNX:

• No errors from overlapping frame ICP alignment.
• No errors from sequential scan positions ICP alignment.
• Good relative accuracy for segments of 500 m.

ILRIS:
• No errors from GPS outage or poor satellite conditions.
• No errors from attitude compensation.
• Excellent relative accuracy for each frame.
• Lifting device can lower accuracy with bad weather conditions.

Productivity

LYNX:

• Field works: Dramatically faster (1 day vs months) and safer.
• Faster alignment and georeferencing of datasets.
• Significantly faster and easier noise cleaning.
• Automated feature extraction tools work better with uniform density homogeneous pointclouds.

ILRIS:
• Easier manual feature collection with shaded organized pointclouds.
• Advanced filtering techniques work only with organized pointclouds.
• Better level of detail for close objects (resolution – viewing angle).

Related Videos
http://www.youtube.com/watch?v=8_P6qQDDPiM
http://www.youtube.com/watch?v=pK1wqphi1lY

Tarmac 3D modeling and deformation analysis of airplane roundabout loops / Athens International Airport "El. Venizelos" - Greece

Purpose
The airplane traffic at the Athens International Airport towards its 2 air-corridors (eastern and western) is regulated through 4 roundabout loops, 2 for each corridor. Due to the traffic load, the fact that the heavy aircrafts often have to stop at the loops and the type of the pavement, the tarmac at those 4 areas has developed noticeable deformations. So, the technical department of the A.I.A., in order to define the extent of the damage and decide what kind of corrective actions should be taken (from simple tarmac repairs to full pavement reconstruction), requested a detailed 3D modeling of the tarmac surface, followed by a complete deformation analysis. The methodology should combine a high level of detail (measurement every 2-3 cm), speed (each loop could remain closed only for a few hours) and accuracy (<1cm for elevations).

 

Project tasks
• A 3D laser scanning survey, using the Optech ILRIS 36D Laser Scanner, was performed (6 to 9 scan positions per area,   scanner on top of a car, tripod mounted, 20% pan-tilt base overlap, distance between scans <50m).
• Georeference was obtained using conic and circular targets, measured from the airport’s geodetic control points.
• An aligned and georeferenced pointcloud for each area was created.
• Sub-sampling (3cm) and triangulation of data points was performed, followed by an optimization and decimation of the model   from 3 million triangles to less than 5000 triangles, with insignificant elevation information loss.
• An elevation map (contour spacing 2cm) was generated for each area.
• Cross sections were extracted based on the above models and deformations were properly detected, measured, demonstrated   and presented in table reports.
• Results have been evaluated by the A.I.A. technical department and different corrective actions have been decided for each loop   area.

 

Results - Conclusions
Laser scanning has proven to be not only the most effective method for the project's purposes, but in fact the only one applicable, offering the required resolution / level of detail and accuracy at a speed that was acceptable for the airports restrictions.

 

Related Videos
http://www.youtube.com/watch?v=LBW62dvUBOc

3D survey and structural deformation analysis of Axios river bridge
at Northern Greece

Purpose
Close to the city of Thessaloniki, in Northern Greece, the Patras - Athens - Thessaloniki - Evzoni (P.A.TH.E.) Motorway, which is the main from South to North road transport axis of Greece, crosses the Axios river, one of the largest of the wider Balkan area. The crossing occurs with two long bridges, each carrying one carriageway. The southern bridge was constructed first about 40 years ago, while the northern one is much newer.

 

The southern bridge is 780 m long with 25 spans, built from armed concrete and has begun to show noticeable damages through time. The Greek Ministry of Environment, Planning and Public works assigned a project to check the bridges efficiency. Within the frame of this project, a complete 3D survey and deformation analysis was required.

 

Project tasks
• Establishment of geodetic network (GGRS’87).
• TLS survey with Optech ILRIS36D:
• 6 scanning positions (from newest bridge)
• Average resolution 2-3 cm
• Georeferencing: 6 scanning stations, 12 circular (d:50 cm) targets, additional “natural” control points
• Conventional survey for remaining details (southern side).
• Basic processing of TLS data and other measurements.
• 3D features collection (deck geometry, piers, road level, etc).
• Geometric evaluation and deformation analysis.

 

Results - Conclusions
To better evaluate the 3D deformations of the bridge components, the results were presented as a longitudinal section of all examined deck edges, as well as angular measurements for each pier along the 3 axis, to demonstrate possible pier rotation. The evaluation showed insignificant rotations for the piers, but surprisingly revealed considerable subsidence of all piers, except those which were founded in the river's bottom. Different type of foundation was identified as the most possible cause for this problem. Corrective actions are being studied to prevent further damage and deformation of the bridge's structure.

 

Related Videos
http://www.youtube.com/watch?v=etVXdPB3uRU


Railway tunnel survey and structural inspection
Aghios Stefanos, Athens - Greece

Purpose
The Greek Railway Organization main railroad, to its northern exit from Athens, passes through a tunnel complex, consisting of four tunnels (two for each railway line), near the small city of Aghios Stefanos. The NE tunnel, approximately 200m long and 5m wide, was built from stones about 50 years ago. Due to suspected deformations of this tunnel in combination with known geological problems of the whole area, the Greek Railway Organizations ordered a stability check, along with a complete survey of the tunnel and the superjacent ground.

 

Project tasks
Establishment of geodetic network (GGRS’87).
TLS survey with Optech ILRIS36D:
• 8 scanning positions (6 inside – 2 outside)
• Average resolution 1-2 cm
Georeferencing: 8 conical targets, additional control points
Conventional survey of superjacent ground surface above tunnel.
Basic processing of TLS data and other measurements.
3D modeling of tunnel and superjacent ground, H and V section extraction.
Inspection in comparison to theoretical geometry.

 

Results - Conclusions
The cross-section based evaluation and comparison of the surveyed tunnel wall to its theoretical geometry revealed large deformations at specific locations (e.g. section 15). These locations have been defined and mapped in detail and repairing actions have been designed. Tunnel has been closed until repair works will be executed. Further geological investigation defined the reason of the deformations to be the presence of slate (sch) and clay (PT) formations at the tunnel's area and the existence of a possible fault between them.  

 

Related Videos
http://www.youtube.com/watch?v=ZXj6yJXjXZo