L1: Introduction to Surveying Flashcards
Why is surveying important (how is it used)?
1) map of the Earth
2) prepare navigational charts
3) establish property boundaries (of private and public lands)
less important:
4) develop data banks of land-use and natural resource info (help manage the environment)
5) determine facts on size, shape, gravity, magnetic fields of Earth
6) prepare charts of moon and planets
Define surveying (in general)
The art and science of taking field measurements on the surface of the Earth
Define surveying (in the engineering context)
The process of measuring lengths, heights, and angles on site; either for the preparation of large-scale plans or in order that engineering works can be located in their correct positions on the ground
Define geomatics
The modern discipline which integrates the tasks of gathering, storing, processing, modeling, analyzing, and delivering spatially references or location information
(including the computerization and digitalization of data collection, processing, and analysis)
What do geomatics engineers do?
Design, develop, and operate systems for collecting and analyzing spatial information about the land, the oceans, natural resources, and manmade features
Define remote sensing
The acquisition of information about an object without making physical contact with the object
What is the difference between an active sensor and a passive sensor in remote sensing?
Passive sensors: use electromagnetic waves from an external source (such as the sun)
Active sensors: produce and use their own waves
What are two different satellite orbits (briefly describe each)?
Geostationary: satellite stays over the same point on the surface through its orbit
Quasi polar: satellite loops around the poles to cover the entirety of Earth’s surface
What is orthophotography and how does it apply to airborne surveying?
In some airborne surveys, photos are taken from a plane
These photos will be deformed due to the perspective of the camera
Through orthophotography, an accurate picture can be found from combining photos from multiple perspectives
Define GIS
A computer system for capturing, storing, checking, and displaying data related to positions on Earth’s surface
What are the four main functions of GIS?
1) Data management for storing geographic locations
2) Visualizing geographic data (typically using maps)
3) Analyzing spatial relationships and patterns using geoprocessing
4) Creating new data or editing existing data
Define geodesy
The science of measuring and understanding Earth’s geometric shape, orientation shape and gravitational field
What are the three models of the Earth’s shape in order of increasing accuracy?
Least accurate: spheroid
Ellipsoid
Most accurate: geoid
Define geoid
The equipotential surface that most closely approximates to mean sea level in the open oceans
Why are all map projections inaccurate?
It is impossible to accurately represent a geoid (or even a spheroid for that matter) on a 2D surface
What is the difference between a geodetic and plane survey?
Geodetic surveys take into account Earth’s curvature (preforming calculations on an ellipsoid)
Plane surveys do not consider Earth’s curvature (performing calculations as if Earth were flat)
List the six main types of surveying (briefly defining each)
GEODETIC: covering such large areas that Earth’s curvature must be accounted for
TOPOGRAPHICAL: establish the position and shape of natural and man-made features over a given area (usually for cartography or GIS)
PHOTOGRAMMETRY: using photographs with special cameras on aircraft (in pairs, they produce 3D images of ground features)
HYDROGRAPHIC: gather info on marine environment (map coastlines and sea bed for navigational charts)
CADASTRAL: establish and record boundaries and ownership of land and property
ENGINEERING: any survey work carried out in connection with the construction of civil engineering
What are the survey field measurements and the instruments often used to perform each?
1) Horizontal and slope distances (tapes, electronic instruments)
2) Vertical distances / heights (levels)
3) Horizontal and vertical angles (theodolites)
Define control surveying
Surveying that is used to establish highly precise positions and elevations to be used as references for other surveys
You obtain a network of points with highly precise position and elevation
Define detail surveying
Surveying that is used to determine and locate the features and improvements on a section of land
What is the difference between a passive control mark and an active control mark? Which one is more advantageous and why?
Passive control marks are controls that are physical objects (such as a metal disk or rod) that cannot alert of movement; once their coordinates are measured once, they are not recalibrated for many years; they are often disturbed, damaged, or destroyed over time
Active control marks have receivers that are constantly collecting and updating information on how they have moved, making them accurate even over time; furthermore, you can use an active control mark from afar, making them more convenient
Overall, active control marks are more advantageous
What is the coordinate system used for surveying?
Cartesian
A plane rectangular system using two axes at right angles
One axis is N, other is E
Scale along both axes is always the same
Take an arbitrary origin at the extreme SW of the surveyed area (no negative values)
What are the four types of north (briefly defining each)?
True north: a fixed point on Earth (the accurate determination of which is only used for special construction projects and not normally in engineering surveys)
Magnetic north: north as determined by a freely suspended magnetic needle; changes with time and place (only used in low-order surveys or to give a general indication of north)
Arbitrary north: any convenient direction chosen to represent north even if it isn’t true or magnetic north (the most commonly used north in engineering surveys)
Grid north: the direction of north based on the National Grid
Define whole circle bearing (WCB)
The angle measured clockwise from N to a line
Same thing as azimuth
