The world is not flat, but it's not round either...
This is the first in a series of 3 blogs that will discuss the various survey levels and how they impact MineRP’s new spatial applications available to the extractive industry.
This blog will discuss geodetic survey followed by planar survey and lastly local survey.
GEOID vs ELLIPSOID vs SPHERE
In order to understand geodetic survey, it is necessary to understand the true shape of the earth. The earth is often described in laymen’s terms as a round ball or sphere and technically as an ellipsoid (rugby ball shape) – neither description is precisely correct. According to Carl Gauss (1818), the earth has a “mathematical shape” called a geoid.by planar survey and lastly local survey.
The geoid is the shape that the surface of the oceans would take under the influence of earth's gravitation and rotation alone, in the absence of other influences such as winds and tides or interruptions such as land mass and mountains. Imagining the earth without mountains or depressions and having equal gravitational pull at all locations will give you the shape of a geoid. It does not correspond to the actual surface of the earth's crust, but to a surface, which can only be known through extensive gravitational measurements and calculations; that is geodetic survey or geodesy.
Geodesy, a branch of applied mathematics and earth sciences is the discipline that deals with the measurement and representation of the earth. These methods recognise the earth’s three fundamental properties; it’s geometric shape, its orientation in space and its gravity field – as well as the changes of these properties in time.
In Geodetic surveying the curvature of the earth, its gravitational field in a three-dimensional time-varying space as well as geodynamical phenomena such as coastal motion, tides and polar motion are taken into account resulting in a higher degree of accuracy in linear and angular observations. The geodetic surveys extend over large areas and lines connecting any two points on the surface of the earth are treated as arcs and angles between these curved lines as spherical angles. For calculating their projected distances on the plans or maps, the correction for the earth’s curvature is applied to the measured distances.
Since geodetic surveys are conducted with the highest degree of accuracy; control points are established on the earth’s surface for subsequent plane surveys. Sophisticated instruments, precise observations and accurate computation allowing for minute adjustments are required to produce control for the next level of survey – planar survey which will be the topic of our next blog.
The transformation of co-ordinates between planar/local systems and geodetic systems is complex and complicated. A variety of factors (physical location on the earth, datum plane, angular- vs. linear co-ordinates, etc.) have to be considered. The recent advances in MineRP’s spatial offerings prompted the company to make provision for the impact of transformation in future developments.