Co-ordinate systems Flashcards
Lecture 3
y and x
latitude (y) and longitude (x) co-ordinates
what are latitude and longitudes measurements of?
geographic co-ordinate system
what is longitude?
measured angle subtended from the centre of the earth to the surface of the earth, east and west of the greenwich meridian - prime meridian (0)
longitude values range from?
180degrees E to 180 degrees W
what is latitude?
anfle subtended from the centre of the earth North and south of the equator (0)
from North to south.
latitude values range from?
90N to 90S
Define the graticule.
A planar grid system of intersecting latitude and longitude lines.
how to the positives and negative of longitude and latitude change with the position around the equator and greenwich meridian?
NW- +latitude -longitude
SW- -latitude -longitude
NE- +latitude +longitude
SE- -latitude +longitude
how do we convert DMS to DD?
(degree + min/60 + sec/3600)
NB 1degree =60min
60 min = 3600sec
what is problem with the shape of the earth?
oblate spheroid - need to make a model of earth to be able to meausure it.
what is a model?
a simplified idealised representation of reality
What are the 3 surfaces to consider, deciding on the best model for earth?
True earth surface
Geoid (mean sea level)
ellipsoid
What is the ellipsoid model?
Mathematical represenation of the earth
reference for depicting geographical co-ordinates
a - equitorial axis
b- from poles the centre.
different ellipsoids work better to depict different parts of the earth.
Not a universal model.
What is a datum?
mathematical model of the Earth
erves as a reference for calculating the geographic
coordinates of a location.
A datum consists of two components:
1. A reference ellipsoid
2. A reference point or location
The further the distance of a location from the reference point of
a datum on an ellipsoid, the greater the geometric distortion of
those geographic coordinates
What was the old datum for South Africa?
Cape Datum
Modified Clarke 1880 reference ellipsoid
Initial point - Buffelsfontein, PE