Page | 10
1.2 Principles of Geodesy – The forgotten Earth science!
Why“ h Fogo nE h c nc ”? c us h s p dng gno nc of hssc nc ,bu n lluson h s inherently understood! (Daniel Boorstin)
1.2.1 Geodesy Geophysics and Geology – is a study of the Earth. We use models as the other two disciplines do, and make adjustments for distortion and errors in those models. G od syp o d s h ‘f m of f nc ’fo llgoodm ps. s h m nsbywhchw c npu og h llso sof different data attributes and ensure that they are correctly juxtaposed. So while we are interested in the relative position of one piec of d o no h , h m ns by wh ch h s s ch d s houghpo dng n‘ bsolu ’ framework or set of rules that ensures that we can do this correctly. Geodesy is rightly then to be considered the underlying and immutable doctrine required to nsu h m ps ( h c og ph s ‘ ’) p op ly p s n h l world they are designed to portray.
Geodesy is defined as the study of:
the exact size and shape of the Earth
•
• the science of exact positioning of points on the Earth (geometrical geodesy) • the impact of gravity on the measurements used in the science (physical geodesy) • Satellite geodesy, a unique combination of both geometrical and physical geodesy, which uses satellite data to determine the shape of the E h’s g o d nd h pos on ng of po n s.
Let us return to the ellipsoid that we studied in the p ous s c on (fgu 5). hs m , h ‘cu w y’ qu d n of h llpsodsow c ns h centre. On this diagram we can see two coordinate systems. One is the Latitude, Longitude and Height of pon ‘ ’ nsp c bo h llpsodsuf c ( could just as well be below). The other is a three dimensional Cartesian coordinate system where X is in the direction of the Greenwich meridian in the equatorial plane, Y is orthogonal to the Greenwich meridian and Z is parallel to the polar axis (orthogonal to the other two axes). The Cartesian system is directly referenced to the ellipsoid centre, the geographic system is directly referenced to the ellipsoid surface and indirectly to the ellipsoid centre. However, both systems are valid and both describe in dff n ‘numb s’ h coo dn sof h pon ‘ ’.
The relationship between the two systems is per the following algorithms:
Figure 5: Ellipsoid coordinate reference systems.
X = (ν + h) * cos φ * cos λ Y = (ν + h) * cos φ * s n λ Z = [(b2 * ν/ 2 ) + h] * s n φ
(wh ‘ν’ s h dusof h llpsod
).
Made with FlippingBook flipbook maker