Basic Geodesy.pptx .........................

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1. Basic Geodesy Principles of Cartography

2. Basic Geodesy Geodesy is the science of accurately measuring and understanding the Earth's geometric shape , orientation in space, and gravity field . Geodesy is the science of the measurement and mapping of the earth’s surface. A branch of applied mathematics concerned with the determination of the size and shape of the earth and the exact positions of points on its surface and with the description of variations of its gravity field.

3. Important Facts about Earth Third planet from Sun 5 th largest planet in the Solar System According to NASA’s (National Aeronautics and Space Administration) Goddard Space Flight Center, Equatorial Radius of Earth is is 3,963 mi. (6,378 km). While as Polar radius is 3,950 mi. (6,356 km) — a difference of 13 miles (22 km). Moreover, Equatorial circumference of Earth-24,901 mi. (40,075 km). and Meridional circumference of earth is —24,860 mi. (40,008 km.

4. Popular Concepts regarding Shape of Earth 03 most popular and ever more accurate approximations about the shape of Earth: Spherical Ellipsoidal Geoidal

5. Spherical Earth A sphere is a perfect round body or an object which is three dimensional, It is the set of all points in three-dimensional space lying the same distance (the radius) from a given point (the center). This concept existed in ancient times that the earth is perfect sphere )a round body whosr radius is same in all directions). This concept was first ever claimed by Greeks more than 2000 years back by various Greek Scholars Pythagoras, Aristotle, Eratosthenes etc. The Concept remained popular till 16 th century. But in fact, Earth is not perfect sphere, rater it is slightly ellipsoidal in shape. But Cartographers still use a same surface area as the ellipsoid called an Authalic sphere as a basic figure of mapping. According to this Earth’s Radius is 6371 km(3959mi or 250,842,240 inches) And the Earth’s Circumference: 40,030.2 km(24,845.1)

6. Ellipsoidal Earth Unti 16 th century the earth was thought to be perfectly spherical in shape. Actually Earth is not perfect sphere rather slightly flattened from pole and bulged from the equator and for this reason it is called oblate ellipsoid or oblate spheroid . This concept was first ever claimed by Isaac Newton in 17 th century. From 1800 till present, at least 20 determinations of the earth’s radii and flattening have been made from measurements taken at widely different locations. For mapping purpose 11 different ellipsoids are used as the basis of mapping in various parts of the world.

7. Continued The WGS (world Geodetic Systems) 72 and WGS 84 ellipsoids , determined from satellite orbital data are considered more accurate than the earkier ground measurement determinations. But they may not give the best fit for a particular part of the earth. The Clarke 1866 ellipsoid, is based on measurements taken in Europe, India , Peru,, Russia, and South Africa is of spherical interest in the United States and has been used for mapping until now, North American cartographers are now rapidly switching to the WGS84 elliposoid , which is considered to be a global standard now.

8. Geoidal Earth An even more faithful figure of the earth is called the Geoid ( meaning Earth like). It is slight deviation from ellipsoid in an irregular manner The Geoid is the Three-dimensional shape that would be approximated by mean sea level in the ocean. Technically, it is a sea level equipotential surface “ the surface on which gravity is equal to its strength at mean level. The deviation is up to 100 meters at certain locations e.g. the highest point on the geoid is 75 meters above the ellipsoid in New Guinea and lowest point is 104 meters below at the southern tip of India.

9. Cartographic use of Sphere, Ellipsoid and Geoid Cartographers use these three approximations to the earth’s true shape in different ways. Authalic Sphere is a reference surface for small scale maps of countries and continents and larger areas, since the difference between sphere and ellipsoid is negligible when mapping large areas in order to avoid complexity in map projection equations. There is also a significant increase in the complexity of map projection equations for ellipsoid. Furthermore, for making large scale maps of small areas particularly topographical maps or nautical charts, ellipsoid (WGS 84 etc.) is used as a reference surface as more accuracy is required and the difference between between locations on the spherical and ellipsoidal approximations can be significant, thus it important to take the earth oblateness into account. While as, Geoid is the reference surface for ground surveyed horizontal and vertical positions and so on.