Lecture #2 Flashcards
What shape is Earth?
Oblate
What is Geodesy?
The study of the shape of the Earth
What are ellipsoids?
A sphere that possess variable radius’ from the centre providing a better representation of a sphere
What is a geoid and how are they captured?
The geoid is the shape of the earth using gravitational data
What is mean sea level used to describe?
Describes the shape of the planet to refer to geodetic
What is a datum?
A reference point in which position measurements are made from
What is a geodetic datum?
A reference to use and determine the size and shape of the earth and coordinate system
What is a geocentric datum?
When the centre mass of the earth is aligned to the centre of an ellipsoid
What is a reginal datum?
When there is an offset between the geoid and ellipsoid
What is a geocentric and regional frame of reference and what are both good at representing?
A geocentric F.O.R . is a good approximation for the geoid while the regional is best used in a regional context
What is NAD27?
A regional datum used in 1866 based of a reference ellipsoid
What is NAD83?
A geocentric datum based of a reference ellipsoid from 1980. GPS is based of NAD83 (WGS83)
What is the problem with using the wrong datum?
The incorrect system will result in mapping errors
Name two coordinate systems
Planar and Latitude/Longitude
What are the disadvantages and advantages of using each coordinate system?
Planar is convenient but least accurate while Lat/Long is least convenient but most accurate
What is the geographical grid?
The geographical grid is used to determine the location of things on a latitude (horizontal) and longitudinal (pole connecters) system
What is the degree of longitude at the equator and how does this differ the closer you get to the equator?
A degree of longitude is 111km at the equator and it gets smaller as you go farther from the equator because they end up meeting at the poles
How do you convert decimal coordinates to degrees, minutes and seconds?
If degree is 30.4545, you follow this equation
30 degrees = 30 degrees
(0.4545x60) = 27.27 = 27 minutes
(0.27x60) = 16.2 = 16 seconds
Why might we use planar maps?
The angles are more simplistic and UTM uses planar
What is UTM?
A way of dividing the earth into 60 longitudinal zones and 20 latitude zones
How does UTM work
Each degree of longitude is 6 degrees wide and it covers the earths surface. You will encounter them in datums and projections
What is a projection?
A transformation of earths surface into a flat surface where all meridians and parallels, human and physical features are transformed in the process
What is the significance of map projections?
Distortion is inevitable, although the projection you use should distort the least important parts and amplify the focus
