Location, Location, Location or Where am I

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Location, Location, LocationorWhere am I?
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The Earth is

• 3000 BC Babylonians 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
• Spheroid
• Geoid to describe the deviations from a spheroid

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How Erastosthenes computed the circumference of
the Earth
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Earth Shape Sphere and Ellipsoid
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Earth as Oblate Ellipsoid
Flatter, longer
Curved, shorter
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The Spheroid and Ellipsoid

• The sphere is about 40 million meters in
  circumference.
• An ellipsoid is an ellipse rotated in three
  dimensions about its shorter axis.
• The earth's ellipsoid is only 1/297 off from a
  sphere.
• Many ellipsoids have been measured, and maps
  based on each. Examples are WGS84 and GRS80.

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Earth as Ellipsoid
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The Earth as a Geoid
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Geographic Coordinate System

• Parallels
• Meridians
• Great and Small Circles

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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.
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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.

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Great Circles

• ..are imaginary circles of the surface of the
  earth whose plane passes through the center of
  the earth.
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• The circumference of the earth is 25,000 miles or
  40,000 km
• "Great" because it is the largest possible circle

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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.

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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 3649'52" N
• ArcMap uses Decimal Degrees
• Sextant measures the angular distance between 2
  points (sun horizon)
• So its easy to determine latitude.

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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.
• Longitude is the angular distance east or west
  from Greenwich, England
• (0 180 degrees E or W)

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The Prime Meridian (1884)
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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

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How to convert from DMS to DD

• Example 373630
• 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

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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

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How the Earth is Divided

• Hemispheres Northern, Southern, Eastern, Western

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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.

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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
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Time Zones