Embed Size (px)
Citation preview
Introduction toIntroduction to terrestrial laser scanningg
African Cultural Heritage and Landscapes Project
Roshan Bhurtha and Christoph [email protected], [email protected]@g , @
Roshan Bhurtha - UCT
IntroductionIntroduction
• LASER is an acronym for Light S s a ac o y o g tAmplification by the Stimulated Emission of RadiationEmission of Radiation.
Roshan Bhurtha - UCT
Safety of laser beamsSafety of laser beams
• Are laser scanners dangerous ?e ase sca e s da ge ous
• Laser devices classified according t th i t tto their power output.
• Terrestrial laser scanners are considered low risk, but precautions must still be takenprecautions must still be taken.
Roshan Bhurtha - UCT
Pictures of laser scannersPictures of laser scanners
• Leica HDS 3000Pictures of laser scanners e ca S 3000
• Medium rangeTerrestrial laser scanning
What do we get out of the laser scanner?
fExample of points cloud
Types of 3‐D terrestrial laser scanning technology
Pulsed time of flight
Phase‐shift based scanner
Data set managementData set management
Roshan Bhurtha - UCT
Pictures of laser scannersPictures of laser scanners
• Leica HDS 4500e ca S 500
• Short range
Roshan Bhurtha - UCT
Roshan Bhurtha - UCT
Terrestrial laser scanningTerrestrial laser scanning
xi,yi,zi & intensityxi,yi,zi & intensity
Point cloudo c oud130 000 scan points at a
10 mm scan interval.
Roshan Bhurtha - UCT
Terrestrial laser scanning1Terrestrial laser scanning
1 – Diagram taken from: Terrestrial Laser Scanning. R Staiger.
What do we get out of the laser scanner?What do we get out of the laser scanner?
• Scanners focus laser beam along the X and Y axis
• Scanner records range intensity and scan angle of each• Scanner records range, intensity and scan angle of each measurement
• Location of each measurement calculated very accurately (in local reference frame)local reference frame)
• Creates an extremely dense, accurate model of the scanned surface
• Each point in the cloud has X, Y, Z and I (intensity)
• A low power laser beam is used to measure the position of points on an object in 3‐dimensions. As time progresses, several readings are taken and a 3‐D map of the surface is created.
• The scanner is manually moved around the object to measure points from many different angles, so that we get a full coverage of the object.
Roshan Bhurtha - UCT
Example of points cloudExample of points cloud
• The Summer House e Su e ouse
Roshan Bhurtha - UCT
Roshan Bhurtha - UCT
Roshan Bhurtha - UCT
Roshan Bhurtha - UCT
Types of 3‐D terrestrial laser scanning technologyTypes of 3 D terrestrial laser scanning technology
• Pulsed time‐of‐flight(Medium‐Long range)u sed t e o g t( g g )
• Phase‐shift based (Short range)
Roshan Bhurtha - UCT
Pulsed time of flight
Roshan Bhurtha - UCT
Pulsed time‐of‐flight 2
• Distance = speed * time sta ce speed t e
• 2 * R = c * t
• R = (c * t) / 2
• R = RangeR Range
• c = speed of light ( 3 x 10e8 m/s)
• t = round trip time for light pulse
Roshan Bhurtha - UCT
Phase‐shift based scanner
• Time of flight tL is measured by the e o g t tL s easu ed by t ephase difference between the transmitted signal and receivedtransmitted signal and received signal.
Roshan Bhurtha - UCT
Phase shift based – 2Phase shift based 2
Roshan Bhurtha - UCT
Phase‐shift based scanner2Phase shift based scanner
• Based on phase comparison method• EDM transmits a coaxial intensity modulated optical measuring beam that is reflected off a targetis reflected off a target
• The phase difference between the transmitted light and the reflected light g grepresents a distance
• Only the phase offset is obtained from th h ithe phase comparison
• Cycle ambiguity is resolved using multiple measurement modulation wavelengthsmeasurement modulation wavelengths
• Provides a unique integer number –distance to target calculatedg
2 Laser Scanning: TECHNOLOGY, APPLICATIONS and BENEFITS. Mark Smith.
Data set managementData set management
• Scanner generates large amounts Sca e ge e ates a ge a ou tsof data
60 MB f d t f S H• 60 MB of data for Summer House
• Others can generate as much as 10 gGB!
Roshan Bhurtha - UCT
Thank YouThank You
Roshan Bhurtha - UCT
