25 (26) GNSS questions Flashcards
(26 cards)
What is the Geoid
The geoid is an equipotential surface that corresponds with the mean sea level to take into account the mountainous or flatter land areas to estimate the shape of the earth.
What is the Ellipsoid
The ellipsoid is a mathematical shape that describes the earth’s surface as a best fit, however doesn’t take the topography of the earth into account.
Map projections used by OS for the UK
The map projections used by the ordnance survey (OS) is a modified transverse Mercator projection.
OSGB36
The OSGB36 is a datum used by ordnance survey based on a transverse Mercator projection of Airy’s ellipsoid.
OSTN15
OSTN15 is a transformation model used to convert between OSGB36 the UK national coordinate system and ETRS89 a European coordinate system.
OSGM15
OSGM15 is a transformation model used to convert geodetic heights (ellipsoid) to orthometric heights (mean sea level).
Types of heights
Three different heights are ellipsoidal height, orthometric height and geoidal height; the most commonly used is the orthometric height.
GNSS
GNSS stands for global navigation satellite system.
Reference system for GNSS positions
GNSS positions are usually expressed in the WGS84 (world geodetic system 1984).
European satellite system
The name of the European satellite system is Galileo.
National Mapping Agency for the UK
The National Mapping Agency for the UK is the ordnance survey (OS).
RINEX file
A RINEX (receiver independent exchange format) file is a format for raw satellite navigation system data from GNSS and can be found from sources such as international GNSS service (IGS).
Network RTK
A RTK (real time kinematic) VRS (virtual reference station) network is a system of reference stations that are used to provide real-time corrections to GPS data to enhance accuracy and efficiency.
Fundamental positioning process in GNSS
The fundamental positioning process used in GNSS coordinate determination is trilateration.
Mitigating ionospheric error in GNSS
To mitigate ionospheric errors in GNSS positioning, techniques like dual-frequency receivers, Precise Point Positioning (PPP), and Real-Time Kinematic (RTK) can be employed.
Autonomous GNSS positioning
Autonomous or standalone GNSS operation uses radio signals from GNSS satellites alone. No other sources of augmentation or correction are used in the position computation.
Geoidal separation
Geoidal separation, also known as geoid undulation, is the vertical distance between the geoid (mean sea level) and the reference ellipsoid used in GNSS systems, such as WGS84.
Site calibration or localization
Site calibration, also known as localisation, is a process used in surveying and GPS/GNSS projects to align or transform GPS data with a local, project-specific coordinate system.
UK national height datum origin
The UK national height datum was originally based in Newlyn, Cornwall.
UK National Grid map projection
The UK National Grid is based on a Modified Transverse Mercator projection.
Minimum satellites for GNSS position
A minimum of four satellites are needed in order to establish a GNSS position.
Segments of GNSS
GNSS is comprised of three segments: the space segment, the control segment, and the user segment.
Distance measurement in GNSS
Distances (ranges) are measured by measuring the time it takes for a signal to travel from a satellite to the receiver.
Integer Ambiguity
The Integer Ambiguity is the unknown number of full wavelengths present in the phase measurement between a satellite and a receiver.
