Faculty of Applied Engineering and Urban Planning Civil Engineering Department Introduction to Geodesy Introduction Lecture 1 Week 2 2 nd Semester 2008/2009

Why do we need to study Geodesy?! EarthMap Mapping is done based on surveying

1.In surveying, what we are doing is mapping a certain “parcel of the surface of the earth”… 2.For us to “put together” these parcels of the surface of the earth and place them on their correct positions to come up with a meaningful representation…. that is a map…. 3.We need to reference our surveys and position them into to a common space…into an imaginary model of the earth… 4.Referencing and Reference Systems for mapping purposes is the ultimate task of geometric geodesy Again, why do we need geodesy?

Earth Map Surveying Reference Model/System Mapping Integration A complex, dynamic, immeasurable “object” A discrete, measurable, understandable object

A reference system is a defined surface in which we “refer” (position) all our surveys or mapping activities. Reference System

1.Reference Ellipsoid 2.Coordinate Systems 3.Control Network 4.Geoid Model 5.Positions and Positioning Methods And, what do we need to reference our maps …

Questions?!

Geodesy came from the Greek words “geo” ad “desa” means…. “earth” and “ to divide”. Webster defines geodesy as.. “that branch of applied mathematics which determines by observation and measurement the exact positions - points and the figure and areas of large portion of the earth’s surface - the size and shape of the earth, and the variations in the terrestrial gravity” Definition of Geodesy

The classical definition of geodesy is… “the science of measuring and portraying the Earth’s surface” (F. R. Helmert, 1880) The contemporary definition of geodesy is … “the discipline that deals with the measurement and representation of the Earth’s surface, including its gravity field, in a three-dimensional time varying space” (Vanicek & Krakiwsky, 1986) Definition of Geodesy

All the definitions of geodesy will include three general ideas or concepts: 1.the size and shape of the earth 2.the gravity field of the earth 3.the positioning of points on the surface of the earth Concepts of Geodesy

Geodesy and Other Sciences

Branches of Geodesy Physical Geodesy Geometric Geodesy Geodetic Astronomy Satallite Geodesy

Dating back to the Sumarians 5000 years ago when man first became interested with his surroundings. It all started with the concern of what is “my house’s immediate vicinity” Later it expanded to the distances of markets and exchange places With the development means of transportation, man became interested in his “whole world”. History of Geodesy the oldest among the earth science

It was the shape that comes first…. began with the Greeks (Homer) theorizing the earth as a “flat disc” Anaximenes thought the earth as a rectangular object Next was the view of earth as sphere but exactly when the notion of a spherically shaped earth first came into existence is not known. However, recorded history reveals that as early as the sixth century B.C., a Greek philosopher by the name of Pythagoras believed the earth was not flat but round. The Story of Earth’s Size and Shape… the mother of Geometric Geodesy

Three centuries later, Aristotle ( B.C.) considered the idea of a round earth as he studied the movement of planets. From his observations, particularly those of lunar eclipses, he concluded that the earth was indeed spherical in shape. The Story of Earth’s Size and Shape… the mother of Geometric Geodesy

after the shape, the size came in….. the first approximation of the earth’s circumference was proposed by Plato at 40,000 miles then Archimedes approximate it at 30,000 miles. Meanwhile around 250 B.C., in Egypt, a Greek scholar and philosopher, Erathosthenes, set out for a more explicit measurement of the size of the earth The Story of Earth’s Size and Shape… the mother of Geometric Geodesy

Eratosthenes developed a simple method for calculating the earth’s circumference. Using a knowledge of the sun’s position relative to the earth and some principles of geometry, he calculated the earth’s equatorial circumference to be 25,000 miles. The Story of Earth’s Size and Shape… the mother of Geometric Geodesy

but the search for better figure that defines the shape of the earth continues…. In the 17th century, the theory that earth is not a perfect sphere arises. However, these resulted to an intense controversy between the French and the English The English claimed that the earth must be flattened but the French defended their claim for an egg- shape earth The Story of Earth’s Size and Shape… the mother of Geometric Geodesy

To settle the issue the French Academy of Sciences, in 1735, sent out an expedition to confirm the correctness of the claims. The measurements of the expedition in Peru conclusively proved the earth to be flattened. But the story does not end there… The pear-shaped earth was introduced in view of the gravitational influence on the surface And lastly, the potato-shaped earth was introduced to consider the uneven distribution of masses on the surface of the earth The Story of Earth’s Size and Shape… the mother of Geometric Geodesy

Abu al-Rayhan al-Biruni ( ) father of geodesy Geodesy in the Islamic World

At the age of 17, al-Biruni calculated the latitude of Kath, Khwarazm, using the maximum altitude of the Sun. Al-Biruni also solved a complex geodesic equation in order to accurately compute the Earth's circumference, which were close to modern values of the Earth's circumference. His estimate of 6,339.9 km for the Earth radius was only 16.8 km less than the modern value of 6,356.7 km. By the age of 22, al-Biruni had written several short works, including a study of map projections, Cartography, which included a method for projecting a hemisphere on a plane.

Check out this paper: archive00/termpapers/ghabayen.htm