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Location, Location, Location
Geodesy
The study of the size and shape of the Earth.
The Earth is…
• 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 sphericalsurface to define locationson Earth.
GCS includes an angular unitof measure, a prime meridianand 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)
• 1° of latitude = 40,000 km/ 360°
• 1 degree = 60 minutes
• 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