Lecture 3 Flashcards
What framework is used to represent the Earth?
the geodetic framework (census and postcodes)
Principles of Surveying:
What is all surveying based on?
Triangulation - drawing triangles to determin distances.
Historically used in 1st and 2nd order survey
Principles of Surveying
Bearing?
Distance?
Trilateration?
Bearing - direction or position of something from a fixed point (measured in degrees)
Distance - how far a point is from another
Trilateration - measureing points with circles (most accurate because there are 3 known places)
Principles of Surveying
What are the two types of bearing?
Angle - less than 90 degrees and described in cardinal directions (South East 45 degrees)
Azimust - between 0 and 360 degrees, mesured clockwise
Principle of Surveying
Example of India
Triangulation and triganometry –> provides topographic framework (taxes), big science and shape of Earth
Global Positioning Systems (GPS)
What are the 3 main systems?
Navstar (USA) - 24-32 satelites
Glonass (Russia)
Calileo (Europe)
Global Positioning Systems (GPS)
How does it work?
Through Trilateriation (circles)
Global Positioning Systems (GPS)
Practical accuracy?
On a clear day 15m
Global Positioning Systems (GPS)
Differential GSP
Improved accuracy (65-22cm error per 100m) A type is the OS GPS network which is available to whole country and works through 110 base stations
Coordinate Systems
Uses the…. system?
Geodetic referance system, seeing the world as approximately ellipsoid
GRS80 - geodetic refernace system 1980
WGS84 - World geodetic system 1984
NAD27 + NAD83 - north American
Map Projections
To produce a map Earth must be…
Projected onto a flat plane…
- Cylindrical
- Planar
- Conic
Map Projections
1569…
Mercator Projection
- cylindrical
- Conformal - preserves angles sp useful for navigation
- Sees Earth as Flat
Map Projections
1974…
Gall Peter’s Projection
Equal area map - countires are correct size
Map Projection
R…
Robinsons
Psudeo Cylindrical
Attributes?
Where (latitude and longitude) and What (elevation, census)
