2. Understanding the Key Concepts
Shape of The Earth: Spheroids, Ellipsoid, and Geoid
https://www.youtube.com/watch?v=ThtQwbi8UVo and http://geokov.com/education/datum.aspx
1. Spheroid and Ellipsoid: The Earth is not a perfect sphere .It’s like a
Squashed/Squeezed Sphere in the Pole
Semi-Major Axis
Semi-Minor Axis
3. Understanding the Key Concepts(Ct’d)
To find Precise measurement we base on Ellipsoid which is
sometimes called Spheroid rather than Sphere
2.Geoid: Lumpiness of the Earth +Ellipsoid(Spheroid). Geoid is
the best representation of the Earth because it combines its
real shape and variation of the surface at the same time.
5. Understanding the Key Concepts(Ct’d)
https://www.youtube.com/watch?v=xKGlMp__jog
3.Datum:
6. Understanding the Key Concepts(Ct’d)
Google earth and Most
smart phones display
data(Latitudes and
Longitudes ) using the
WGS Datum
WGS 84: World
Geodetic System was
established in 1984
7. Understanding the Key Concepts(Ct’d)
• There many Datum in use, Almost every country has its own
Datum, WHY?
8. Understanding the Key Concepts(Ct’d
• A datum can be
Global Datum(WGS
84) or local datum
i.e North America
Datum...NAD83
9. Understanding the Key Concepts(Ct’d
• You can look up
the datum or
Position format to
in your GPS
manual for
Information about
changing the
Datum
