TERRESTRIAL LASER SCANNING (TLS):
APPLICATIONS TO ARCHITECTURAL AND LANDSCAPE
HERITAGE PRESERVATION – PART 1
WHAT IS TLS?
• TLS is an integrated suite of three-dimensional
spatial technologies that have significant
applications to the preservation of cultural
heritage across multiple scales.
TLS USES:
 H3D is an innovative and
versatile set of tools for
archaeological research.
 It can be brought to an
archaeological investigation
to assist in the development
of highly accurate models of
the site and the surrounding
landscape.
 It can be used to augment
prior work and to create
accurate maps and models
and to conduct spatial
analysis.
 These methods can help to
eliminate subjective
decisions.
SCALE OF ANALYSIS
SHORT RANGE
Kaminaljuyú
Stela 10
MID RANGE
LONG
RANGE
MORE ON H3D:
• Laser scanning is a non-contact, non-destructive, and
non-invasive method to acquire extremely accurate
high resolution data that can be used to analyze,
model, and monitor architectural structures and
their supporting physical elements.
• Terrestrial Laser Scanning is a primary component of
an H3D approach
ALLIANCE FOR INTEGRATED SPATIAL TECHNOLOGIES, UNIVERSITY OF SOUT H
FLORIDA
EXAMPLES OF LONG AND MID RANGE TERRESTRIAL
LASER SCANNERS
Equipment
Dynamic Range
Level of Accuracy
Points per second
1500 meters
7 mm at 100 m
2,500
300 meters
4-6 mm at 50 m
50,000
70 meters
3 mm at 25 m
120,000
TYPES OF LASER SCANNERS
•
TOF- Time of Flight – short duration burst pulse, used for longer range, less ‘points’
collected.
•
Phase-based scanner – continuous beam, measures the phase difference, used for
shorter ranges (~50 to 100 m), high scan rate and accuracy
•
Triangulation-uses laser light to probe the environment. Shines a laser and uses a
camera to look for the location of a laser dot. Depending on how far away the laser
strikes the surface, the laser dot appears at different places in the camera's field of
view. Called triangulation because the laser dot, the camera, and the laser emitter
form a triangle with a known position. Can be highly accurate, used for short range,
control for environment needed.
•
Structured Light- Structured-light 3D scanners project a pattern of light on the
subject and look at the deformation of the pattern. Highly accurate, perhaps better
with shiny surfaces, high degrees of environmental control needed.
•
Also, handhelds, hybrids and very low cost options
TIME OF FLIGHT LASER SCANNERS
LONG RANGE TERRESTRIAL LASER SCANNING (TLS)
Also called ground based LiDAR
Alliance for Integrated Spatial Technologies
University of South Florida
PHASE-SHIFT SCANNERS
TRIANGULATION
ARCHITECTURE WITH PHASE SHIFT
SCALE DIFFERENCES THAT MATTER
Alliance for Integrated Spatial Technologies
University of South Florida
LIGHT DETECTION AND RANGING (LIDAR)
• Space, Airborne, and Terrestrial laser
scanning
Airborne Laser Scanning (ALS)
• Laser scanner mounted on
airborne platform
• Surface models generated from point
clouds
• Often Integrated with Terrestrial Laser
Scanning (TLS)
Alliance for Integrated Spatial Technologies
University of South Florida
POINT CLOUDS
•
Scanner measures range, azimuth and vertical angle (X,Y, Z plus intensity- and
some can add color images quite easily)
•
Gridded data means that you have uniform point spacing…point clouds have
randomly spaced data
• Point clouds are random (not in a grid) – creates issues for data storage and
analysis – big datasets
•
Grids are more predictable…clouds are so dense that you don’t see points.
•
Huge data sets and increases continuing to be seen in scan rates
• industry keeps increasing speed of scanning, and that increases the size of
datasets captured. Leads to issues in storage, retrieval and management
•
Can be mobile or fixed
POINT CLOUDS
ENVIRONMENTAL CONDITIONS THAT
EFFECT SCANNER RANGE AND QUALITY
(a)
Light – daylight reduces range and
increases noise in scan.
•
(b)
Surface Qualities – shiny, highly
reflective surfaces are difficult to
scan.
•
(c)
Solution: decrease range,
increase angle to object
Color – darker objects reflect less
light.
•
(d)
Possible Solutions: scan
on overcast or evening
conditions; reduce range to
target
Solution: decrease range,
add powder coating,
Movement – Scanner and target
object must both be stationary
FIELD AND
LAB
POSTPROCESSING:
•
Microsoft Windows XP, 2000 (Vista for workstations)
•
1 GHz processor
(2.5 GHz recommended)
•
1GB RAM
(4 GB recommended)
•
Wheel mouse with 2 buttons
•
Graphic card with OpenGL hardware acceleration - 32MByte on board memory
•
Ethernet-card for licensing
POINTS TO CONSIDER:
 What are the short-term and long-term research questions?
 What is the intended use for the data?
• Types of projects
• Cultural sensitivity
• Potential hazards
• Window of opportunity
• Registration
• No registration
• Local registration
• Global registration
• Logistics
• Access to first aid
• Access to the project area
• Availability of Power supplies
• Access to additional materials
• Storage facilities
• Number of personnel required
• Budget
ON-SITE DETAILS:
 Geometry – scanner and
reference target set-up
positions
 Positioning the Scanner
• The scanner will record only
what it can see
• This means that the
references and the target
object must be in the line of
sight of the unit.
• For registration each scan
requires a minimum of 3
visible references; these
references should be evenly
spaced around the scanner.
For better control use 4
references per scan.