Lecture 6

GE 161 – Geometric Geodesy

Introduction to Geodesy: Concepts in Geodesy

The SSystems Systems ystems The Geodetic Geodetic Datum, Datum, the the Reference Reference Systems and and the the Geodynamics Geodynamics of of the the Earth Earth Lecture No. 6 Department of Geodetic Engineering University of the Philippines

a.s. caparas/06

The The Geodetic Geodetic Datum Datum and and the the Geodetic Geodetic Reference Reference Systems Systems • Recall… earth

Clark, GRS, WGS Ellipsoid Choose or define a reference ellipsoid

WGS84, PRS92

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Geocentric or Geodetic

Define the origin Establish control network Determine positions of the control stations

GE 161 161 – – Geometric Geodesy

Define geoid model Define the geoid geoid-ellipsoid separation

Concepts in Geodesy: The Geoid Geoid and and the Height Systems

The The Reference Reference Systems Systems and and Reference Reference Frames Frames • A Reference System - is the conceptual conceptual idea idea of a particular particular coordinate coordinate system; (theoretical definition). • A Reference Frame - is the practical practical realiza realization tion of a reference reference system by observations an measurements (which have errors). • In practical surveying we are only concerned with reference frames, but the underlying concepts of a specific reference frame are of fundamental importance. Lecture 6



The The Geodetic Geodetic and and the the Celestial Celestial Reference Reference Systems Systems and and Reference Reference Frame Frame Geodetic/Terrestrial • Geodetic/Terrestrial Reference System (GRS)/(TRS) - Concep Conceptual tual idea idea of an earthearthfixed Cartesian system (X, Y, Z)

• Geodetic/Terrestrial Reference Frame (ITRF) - Practi Practical cal realizati realization on of a geodetic reference system by observations of terrestrial points Lecture 6

Celestial • Celestial Reference System (CRS) - Conce Conceptual ptual idea idea of an spacefixed Spherical coordinate system.

• CelestialReference Frame (ICCRF) - Practi Practical cal realizati realization on of a geodetic reference system by observations of stars/celestial bodies



The The Global Global and and the the Local Local Geodetic Reference Reference System System • Global GRS Origin: Origi n: Earth´s Earth´s centr centre e of mass mass Z-axis: Coincides with mean rotational axis of Earth X-axis: X-axi s: Mean meridian meridian plane of Greenwic Greenwich h and ± to Z-axis Y-axis: Orthogonal

• Local GRS Origin and orientation of axes is "arbitrary" Lecture 6



The The Global Global and and the the Local Local Geodetic Reference Reference Frame Frame • Global Reference Frame Looking at the definition of a reference frame, there should be only one truly global reference frame (ITRF)

• Local Reference Frames Since each country/area in the surface of the earth uses a frame that is appropriate to the local surface, there are infinite number of local frames. Lecture 6



The The Global Global and and the the Local Local Geodetic Reference Reference Frame Frame

A Global Reference Frame Lecture 6

A Local Reference Frame



What What is is aa Geodetic Geodetic Datum? Datum? • The term term “datum” “datum” is often used when when one actually means “reference frame” • A geodetic datum is expressed in terms of the set of transformation parameters which are required to define the location and orientation of the local frame with respect to the global one. • Minimum set of parameters required to define location and orientation of the local system with respect to the global reference system/frame. Lecture 6



The The Geodetic Geodetic Datum Datum

A geodetic datum is used as reference for computing the positions of a point observed in the surface of the earth for geodetic and mapping purposes at a certain portion on the surface of the earth.

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Geodynamics Geodynamics of of the the Earth • The ITRF as a global reference frame provides position solution accurate within 10 cm at any given. • The maintenance of a datum at this level of accuracy requires constant monitoring of the of the geodynamics of the earth.

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Geodynamics Geodynamics of of the the Earth • Some of the geodynamics being monitored by the IERS for the ITRF: 1. Polar Motion 2. Tectonic Plate Motion 3. Solid Earth Tides 4. Ocean Loading

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