Transcript Location, Location, Location

Location, Location, Location
Geodesy
The study of the size and shape of the Earth.
The Earth is…
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3000 BC Babalonians
An oyster
600 BC Greeks
Flat
500 BC a perfect shape
A sphere
300 BC Circumference
~ 25,000 miles,
Dark ages
Flat again
1492 Columbus
A pear
1753 French
Oblate ellipsoid
Spheriod
Geoid to describe the deviations from a spheriod
The Earth as a Geoid
Geographic Coordinate System
•Parallels
•Meridians
•Great and Small Circles
Geographic Coordinate System
GCS uses a 3-D spherical
surface to define locations
on Earth.
GCS includes an angular unit
of measure, a prime meridian
and a datum.
Locating yourself on a Sphere
• You need a frame of reference
• That is the purpose of Latitude and
Longitude
• Defining these parameters:
– Earth rotates on an imaginary axis ~ North
and South Poles
• Equator: is a great circle that lies
equidistant between them.
Great Circles
• ..are imaginary circles of the surface of
the earth who's plane passes through
the center of the earth.
• The circumference of the earth is
25,000 miles or 40,000 km
• "Great" because it is the largest
possible circle
Great Circles:
• Cut the earth in half and each half is
known as a hemisphere
• Are the circumference of the earth
• Provide the shortest routes of travel on
the earth's surface.
– ** Planes travel in great circles.
– ** We were always taught a line is the
shortest distance between two points - Not
True.
• Small circles: circles whose planes do
not pass through the center of the
earth.
Latitude
• Latitude: is the angular distance north or
south of the equator. (0 –90 degrees N or S)
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1° of latitude = 40,000 km/ 360°
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1 degree = 60 minutes
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1 minute = 60 seconds
36°49'52" N
• ArcView 3.x uses Decimal Degrees only
• Sextant measures the angular distance
between 2 points (sun & horizon)
• **So it easy to determine latitude.
Longitude:
• Longitude: no natural reference point
• In 1884 by International Agreement
Greenwich England was the chosen starting
point.
• This is called the prime meridian or zero
degrees and everything is east or west of that.
• Longitude is the angular distance east or west
from Greenwich, England
– (0 – 180 degrees E or W)
Geographic Coordinate System
• Longitude and Latitude
– Degrees, minutes, seconds
– 1o latitude ~110.5 km
(equator)
– 1o longitude = cosine of the
latitude
– 1 minute of latitude ~1852 m
How to convert from DMS to DD
• Example: 37°36’30”
• Divide each value by the number of
minutes or seconds in a degree
• 36 minutes = .60 degrees (36/60)
• 30 seconds = .00833 degree (30/3600)
• Add it all up
• 37° + .60 + .00833 = 37.60833 DD
The global grid:
• Parallels: lines of latitude, only the
equator is a great circle all other
parallels are small circles (they never
meet)
• Meridians: these are line of longitude
and when joined with its mate half way
around the globe form great circles
• * the distance between meridians will
vary with latitude
How the Earth is Divided
• Hemispheres: Northern, Southern,
Eastern, Western
Time Zones
• Solar noon: most towns used this, defined
as when a vertical stake cast the shortest
shadow.
• By the 19th century transportation and
communications (namely railroads and
telegraph) connected towns and cities, the
adopt of a standard time was necessary.
Time Zones (continued)
• 1884 at the International Meridian Conference 24
time zones were established.
• Greenwich Mean Time (GMT) = Universal time
= Zulu time
• 360°/24 = 15° for each time zone, however for
convenience many time zones follow state and
country lines.
• International Date Line: where each new day
begins 180th meridian
• Chronometer
Time Zones