Laser Scanning Flashcards
What is Laser Scanning?
Active remote sensing technique where they use their own energy source in order to create an image.
What does laser scanning do?
Its a method of directly deriving a cloud of 3D coordinates in order to describe the shape of a surface.
What is laser scanning often incorrectly referred to?
LiDAR
What does LiDAR stand for?
Light Detection And Ranging
What does laser scanning deliver? (5)
1) Point Clouds
2) DEM’s
3) CAD models
4) Volume estimations
5) Line drawings
When is laser scanning used? (3)
1) Civil Engineering
2) Earth Sciences
3) Gaming industry
Define terrestrial laser scanning.
Collects 3D coordinates of a given region of an objects surface automatically in a systematic pattern at a high rate and achieves the result in real time.
What does terrestrial laser scanning consist of? (2)
1) A method to collect the data (the laser scanner)
2) A method to manipulate the data (a software solution)
What are the principles of terrestrial laser scanning?
1) Optical triangulation
2) Time pulse
3) Phase measurement
What is the difference between terrestrial laser scanning and mobile laser scanning?
With mobile you don’t have the scanner static you mount it on a vehicle or wear the equipment.
Name examples of airborne laser scanning? (3)
1) Different sensors such as timed pulse laser and continuous wave laser
2) Helicopter, aeroplane mounted but heavily reliant on GNSS.
3) Full wavelength digitising, Geiger mode/single photon systems.
Why is TLS useful for surveyors?
1) Millions of points in minutes
2) Cost-effective alternative for many land survey projects.
3) Can operate in low light
4) Multiple outputs can be derived from raw data- surface models, CAD outputs, visualisations, etc.
What does Laser stand for?
Light Amplification by Stimulated Emission of Radiation
What does a laser have in it?
Two mirrors:
1) One fully reflective and one partially reflective
2) Generate and maintain energy
What is the classes of lasers based on?
The power and wavelength of the laser.
What lasers are required to have a warning sticker on?
Class 2 or higher.
What do terrestrial laser scanners run through in terms of classes?
Class 1 to a class 3R.
What are the basic components of a laser scanner?
1) Scanner
2) Laptop
3) Tripod
4) Power supply
What are the main characteristics of a time-of-flight systems for laser scanners? (3)
1) Range measured as time lag between outgoing and received pulse
2) Quality of the timer determines the accuracy of the instrument.
3) Suited to large objects and outdoor applications
What are the main characteristics of optical triangulation system for laser scanners? (4)
1) Close range 0 to 2/3 metres
2) High resolution <1mm
3) Hight accuracy <1mm
4) Suited to small objects/features.
Draw the diagram for triangulation, timed-pulse and phase.
See notes.
What does TLS actually deliver?
Coordinate Measurement: Collects polar coordinates (Azimuth, elevation, range), then coverts into rectangular system (x,y,z) and each point is tagged with an x,y,z.
What will the TLS generally add on?
An intensity measurement which is how much reflectance occurs as the laser wavelength interacts with the objects.
What are the coordinates laser scanning delivers?
(x,y,z,i,r,g,b) where:
x,y,z are geometry
i is intensity
g,b is imagery
