3 - Coordinate systems Flashcards
(30 cards)
xy reading also known as
geographic location
Longitude / meridians
The angle subtended from the centre of the earth E/W of Greenwich (Prime meridian, 0degrees)
Range of longitudinal values
180E - 180W
Latitude/ parallels
The angle subtended from the centre of the earth north (N) and south (S) from the equator (0degrees)
Range of latitude values
90N - 90S
(North pole to South pole)
Graticule
A planar grid system of intersecting latitude and longitude lines
NE
+ long
+ lat
SE
+ long
- lat
SW
- long
- lat
NW
- long
+ lat
Lat south of equator
NEGATIVE
Long west of Greenwich
NEGATIVE
On maps / analog coordinates
DMS
GPS coordinates
DDM
GIS coordinates
DD
Oblate spheroid
Earth is wider at equator than at poles
Model of Earth considerations
- True surface of Earth
- Mean sea level (geoid)
- Reference ellipsoid
Major axis A
Equatorial radius
Minor axis B
Poles to the centre
Simplest mathematical model of the earth
Ellipsoid
Datum def
Mathematical model of the Earth & serves as a reference for calculating geographic coordinates.
Components of a datum
- A reference ellipsoid
- A reference point/ location
When is geometric distortion of geographic coordinates largest?
When the distance of a location is further away from the reference point of a datum on an ellipsoid.
Cape reference ellipsoid
Modified Clarke 1880
