Lecture 2: Coordinates Flashcards
What are the three shapes of the Earth?
Sphere, Geoid, Ellipsoid
Describe a sphere
Simple but inaccurate(uses mass center of Earths sphere)
Describe a Geoid
Most accurate model, is slightly irregular/lumpy b/c of density variations in the Earth’s crust (used for geodesy/physics)
Describe an Ellipsoid
More accurate than sphere: slightly flatter at the poles w/a bulge in the middle (equator)
What does equipotential mean?
Every point is at the same potential
What is the equipotential point?
The surface of the Earth’s gravity field which best fits global mean level
How is the Geoid shaped?
Over oceans, Geoid is flat (no currents, no waves). Over continents, is is calculated by gravity measurements
What is topography?
The real Earth’s surface (hills, valleys, plains as we experience them
What is a datum?
A starting point for measurement
What is a horizontal datum?
Known point on the Earth’s surface used for measuring coordinates, distances, and directions
What is a vertical datum?
Known point on the Earth’s surface used for measuring heights
What is a regional datum?
A datum almost every country in the world has to ensure accurate measurements in different parts of the world
What is a goal datum?
Earth centered datums that replace original datums w/a common/more accurate standard
What is the goal for global datums?
To make one system for maps of the entire planet, based on the center of Earth’s rotations
What is Elevation?
Most commonly referenced to Mean Sea Level (MSL)
A height measurements accounts…
for the topography of the earth relative to MSL
What does an Ellipsoid approximate?
The shape of the Earth
What is a Geographic coordinate?
define locations directly on an ellipsoid
What is a Cartesian coordinate?
define locations on a plane
What is Latitude?
Specifies the north–south position of a point on the Earth’s surface (up - down)
What’s is the range of angles for Latitude?
0° at the Equator to 90° North (+) or South (-) at the poles, parallel the equator
What is Longitude?
0° at the Equator to 90° North (+) or South (-) at the poles.
What’s is the range of angles for Longitude?
0° at the Prime Meridian to 180° East (+) or -1800 West (-)
Where is the Prime Meridian?
Greenwich, England
