This document compares highway surveying projects using Optech ILRIS and LYNX laser scanning systems. The ILRIS project involved static scanning over 80 km which took 120 days, while the LYNX project used mobile scanning to cover 240 km in just 1 day. Both systems were able to meet accuracy requirements of 2-3 cm horizontally and 1-2 cm vertically. The LYNX data provided better quality, uniform point clouds while ILRIS allowed for higher resolution of close objects when the scanner was lifted. Overall, the LYNX system provided much higher productivity for highway surveying projects due to its faster, mobile data collection.

1. 4th International
Terrestrial Laser Scanning
User Meeting
Munich, Germany - June 4-5, 2008
ILRIS vs LYNX:
Highway Surveying and Data Post-processing
Michael Xinogalos
Surveying Engineer NTUA
ASTROLABE ENGINEERING / JGC

2. Highway surveying projects
• Korinthos – Tripoli (80 km, ILRIS, 2006-2007)
• Elefsina – Korinthos (60 km, LYNX, 2008)

3. Highway surveying projects
• Concession Self Financing Projects: Construction of a new
highway section / Reconstruction and Maintenance of an
existing highway section
• Existing Highways: Dual Carriageway, 2-3 lanes &
shoulder

4. Highway survey requirements
• 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

5. Korinthos – Tripoli Highway
Project tasks (1/3)
• 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

6. Korinthos – Tripoli Highway
Project tasks (2/3)
• 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, etc.

7. Korinthos – Tripoli Highway
Project tasks (3/3)
• 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 (Polyworks IMAlign -
IMInspect)

8. Elefsina - Korithos Highway
Project tasks (1/3)
• Establishment of geodetic infrastructure networks (triangulation,
leveling, polygonometry), also necessary for construction
• Mobile laser scanning with Optech LYNX Mobile Mapper (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

9. Elefsina - Korithos Highway
Project tasks (2/3)
• Base GPS station support (6 base stations on known points)
• Measurement of positional Ground Control Points (natural targets
identifiable on pointcloud)

10. Elefsina - Korithos Highway
Project tasks (3/3)
• Basic data processing / alignment (SINECO) 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
(Polyworks IMInspect - typical target registration accuracy < 3cm)

11. Both Highway surveys
Post-Processing Project tasks
• Georeferencing refinement for elevations: using additional points
measured on both edges of each carriageway every 50-80m
(Polyworks IMInspect – typical elevation alignment accuracy < 1 cm)
• Feature collection from pointclouds (Polyworks IMInspect)
• 3D Modeling (TIN) from features and Survey Maps (scale 1:500)
generation (Autodesk Civil 3D)
• Archiving for future reference: Pointclouds segmented per km
(Polyworks IMView)

12. Highway survey products
Point cloud vs TIN model / 3D features (ILRIS survey)

13. Highway survey products
Point cloud / 3D features (LYNX survey)

14. Highway survey products
Background survey map (scale 1:500)

15. Highway survey products
Background survey map (scale 1:500)

16. ILRIS vs LYNX comparison (1/3)
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)

17. ILRIS vs LYNX comparison (2/3)
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

18. ILRIS vs LYNX comparison (3/3)
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)

19. Conclusions…
Any questions?
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