Laser Scanning

Question 1

What is Laser Scanning?

Answer 1

Active remote sensing technique where they use their own energy source in order to create an image.

Question 2

What does laser scanning do?

Answer 2

Its a method of directly deriving a cloud of 3D coordinates in order to describe the shape of a surface.

Question 3

What is laser scanning often incorrectly referred to?

Answer 3

LiDAR

Question 4

What does LiDAR stand for?

Answer 4

Light Detection And Ranging

Question 5

What does laser scanning deliver? (5)

Answer 5

1) Point Clouds
2) DEM’s
3) CAD models
4) Volume estimations
5) Line drawings

Question 6

When is laser scanning used? (3)

Answer 6

1) Civil Engineering
2) Earth Sciences
3) Gaming industry

Question 7

Define terrestrial laser scanning.

Answer 7

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.

Question 8

What does terrestrial laser scanning consist of? (2)

Answer 8

1) A method to collect the data (the laser scanner)

2) A method to manipulate the data (a software solution)

Question 9

What are the principles of terrestrial laser scanning?

Answer 9

1) Optical triangulation
2) Time pulse
3) Phase measurement

Question 10

What is the difference between terrestrial laser scanning and mobile laser scanning?

Answer 10

With mobile you don’t have the scanner static you mount it on a vehicle or wear the equipment.

Question 11

Name examples of airborne laser scanning? (3)

Answer 11

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.

Question 12

Why is TLS useful for surveyors?

Answer 12

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.

Question 13

What does Laser stand for?

Answer 13

Light Amplification by Stimulated Emission of Radiation

Question 14

What does a laser have in it?

Answer 14

Two mirrors:

1) One fully reflective and one partially reflective
2) Generate and maintain energy

Question 15

What is the classes of lasers based on?

Answer 15

The power and wavelength of the laser.

Question 16

What lasers are required to have a warning sticker on?

Answer 16

Class 2 or higher.

Question 17

What do terrestrial laser scanners run through in terms of classes?

Answer 17

Class 1 to a class 3R.

Question 18

What are the basic components of a laser scanner?

Answer 18

1) Scanner
2) Laptop
3) Tripod
4) Power supply

Question 19

What are the main characteristics of a time-of-flight systems for laser scanners? (3)

Answer 19

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

Question 20

What are the main characteristics of optical triangulation system for laser scanners? (4)

Answer 20

1) Close range 0 to 2/3 metres
2) High resolution <1mm
3) Hight accuracy <1mm
4) Suited to small objects/features.

Question 21

Draw the diagram for triangulation, timed-pulse and phase.

Answer 21

See notes.

Question 22

What does TLS actually deliver?

Answer 22

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.

Question 23

What will the TLS generally add on?

Answer 23

An intensity measurement which is how much reflectance occurs as the laser wavelength interacts with the objects.

Question 24

What are the coordinates laser scanning delivers?

Answer 24

(x,y,z,i,r,g,b) where:
x,y,z are geometry
i is intensity
g,b is imagery