Wk 4 Flashcards
Define Global position system
satellite-based radio navigation system for determining precise
position and time, using satellite radio signals in real-time or post-processing mode
What does GPS provide?
❑ Latitude, Longitude and Altitude (WGS84)
❑ XYZ coordinated to be used in GIS system
users to determine their exact location,
velocity, and time 24 hours a day in all weather conditions, everywhere in the world.
Three distinct segments of GPS
- Space Segment
- Control Segment
- User Segment
Describe the Space segment of GPS
❑ 31 Satellites
❑ 6 Orbits
❑ 12000 miles (about 20,000 km) above Earth’s Surface
❑ 12 hours Rotation
❑ 4 Satellites visible at a 15° angle anytime
Describe the User Segment of GPS
❑ Anyone with a GPS Receiver
Describe the Control segment of GPS
❑ Control Segment (Operational Control System) is responsible for the proper operation of the GPS system.
❑ The GPS Control Segment is composed by a network of Monitor Stations (MS), a Master Control Station
(MCS), a backup of the MCS and the Ground Antennas (GA).
❑ The control segment tracks the GPS satellites, updates their orbiting position and calibrates and synchronises their clocks
How does GPS work?
trilateration to determine your location. It works by measuring the time it takes for a signal to travel from your location to several nearby satellites
1 satellite can only identify the distance
between you and the satellite, providing a circular range of your location rather than a specific location
3 satellites, it is possible to pinpoint your exact location at the place where all three circles intersect.
the target location is confirmed by the 4th satellite
pros of GPS (5)
❑ It offers a higher level of accuracy than conventional surveying methods
❑ Calculations are made very quickly and with a high degree of accuracy
❑ GPS technology is not bound by
constraints such as visibility between
stations
❑ Land surveyors can carry GPS
components easily for fast, accurate data collection
❑ Some GPS systems can communicate
wireless for real-time data delivery
cons of GPS (4)
❑ GPS land surveying equipment requires a clear view of the sky to receive satellite signal
❑ Interference from dense foliage and other structures can limit function and
communication
❑ All GPS survey equipment is subject to failure from dead batteries and system malfunction
❑ Special equipment may be required and can be costly
what is scan to BIM?
process that involves capturing the physical characteristics of a building or
site using 3D laser scanning technology and converting this data into a BIM model.
This method enhances accuracy in documenting existing structures and facilitates efficient planning for renovations or new constructions
define point cloud
collection of data points in space produced by 3D laser scanners, representing the external surfaces of objects or environments
define 3D laser scanning
technology that uses laser beams to capture the precise geometry of physical structures, generating detailed point clouds for analysis and modelling
define BIM model
A digital representation of the physical and functional characteristics of a facility, serving as a shared knowledge resource for information about a facility throughout its lifecycle
Digital survey in the BIM workflow
(model could be CAD drawing)
define laser scanning
a non-contact measurement technique that captures the shape and spatial data of objects or environments using laser beams.
The technology rapidly collects millions of precise data points, generating a point cloud that represents the scanned surface in three dimensions.
Classifications of laser scanning (4)
classified based on their operational
principles and applications
Terrestrial Laser Scanning (TLS)
Aerial Laser Scanning (ALS)
Mobile Laser Scanning (MLS)
Handheld/Portable Laser Scanning
Define Terrestrial Laser Scanning (TLS)
Ground-based scanning systems used
for high-accuracy 3D mapping of buildings, landscapes, and infrastructure
define Aerial Laser Scanning (ALS)
LiDAR (Light Detection and Ranging) systems mounted on drones, helicopters, or aircraft for large-scale topographical surveys and environmental monitoring
define Mobile Laser Scanning (MLS)
Scanners mounted on vehicles or handheld devices for rapid data acquisition in dynamic environments such as urban streets and tunnels
define Handheld/Portable Laser Scanning
Lightweight, flexible scanners used
for capturing small objects, confined spaces, and real-time 3D modelling
what technologies can TLS be implemented within?
❑ Triangulation (for short-range, high-precision scanning)
❑ Time-of-Flight (ToF) (for long-range scanning using laser pulse travel time)
❑ Phase-Shift (for high-precision, medium-range scanning using phase difference measurements)
how do TLS function
❑ Operated on a tripod
❑ Terrestrial Laser Scanners (TLS)s detect windows like panoramic
in a spherical direction (almost 3D except for small circle base of the tripod)
❑ Point cloud model is the output
❑ TLS(s) are integrated with a camera(s) to colour the point cloud
How do TOF scanners work?
TOF = Time Of Flight
TOF scanners operate by emitting a laser pulse and measuring the time taken for the pulse to return after
reflecting off an object
equation for the distance measured with TOF scanners
what is the rate of which TOF scanners take points?
2M points per second
pros of TOF scanners
Long-range capability (up to several hundred meters)
Fast data acquisition suitable for large-scale surveys
Works well in outdoor environments due to high-power laser pulses
cons of TOF scanners
Lower accuracy compared to phase-shift scanners for close-range applications
More noise in data due to atmospheric variations (e.g. humidity, dust, temperature changes)
High power consumption compared to other laser scanning technologies
fill in the info for TOF laser scanners
fill in the info for total station (EMD)
… control points needed to register … subsequent scans
3 control points needed to register two subsequent scans
post processing data workflow
❑ Registration
❑ Cleaning- selects points you don’t want (autodesk recap)
❑ Segmentation/classification- identifying what is what (e.g. what is wall, desk, floor)
❑ Meshing, Sectioning etc.
❑ Tracing CAD or BIM detail (vectorisation)- importing point cloud into autocad, define space and tracing it
❑ Image-based output
❑ animation/visualisation
it’s actually Tangent Point.
