2.1: TOPOGRAPHY, GEOID AND ELLIPSOID SURFACE *Figure of The EarthMajor tasks of Geodesy : determination size and shape of the earthActual topographic surface: variety of landforms and water areas.-Surface on which actual Earth measurements are made Sphere : close approximation of the true figure of the earth & satisfactory for many purposes.Idea of flat earth : still acceptable for surveys of small areas (

2.1: TOPOGRAPIC, GEODIC AND ELLIPSOIDAL SURFACES *

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B. GEODIC SURFACE*GEOID CONCEPT

GEOID

Equipotential surface of the Earth's gravity field;(approximately) coincides with MSL in the open ocean

The geoid-ellipsoid separations are referred to as geoid undulation or geoid heights or geoid separations.surface of the earth gravity field During the geoid surface, potential ( W) are the same.could be considered corresponding to the global mean sea level

CONT.In geodetic surveying, computation of geodetic coordinates of points is performed on an ellipsoid which closely approximates the size and shape of the earth in the area of survey.

The actual measurement made on the surface of the earth with certain instruments are referred to the geoid.

Geoid forms a suitable reference surface for heights because it is based on the field gravity which governs fluid flow.

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C. ELLIPSOIDAL SURFACE*Ellipsoidal Reference Systems:

Ellipsoid imagination surface that can be used as a basis of reference to describe geoid and the topography surface.

Ellipsoid Geometrical figure used in geodesy to most nearby approximate the shape of the earth is an ellipsoidal models.

Ellipsoid - GPS heights are referenced to this mathematical surface.

C. ELLIPSOIDAL SURFACE*KONSEP Ellipsoid

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C. ELLIPSOIDAL SURFACE*Ellipsoidal Reference Systems:

Reference ellipsoids are usually defined by semi-major (equatorial radius),a and flattening, f (the relationship between equatorial and polar radius)

Flattening indicates how closely an ellipsoid approaches a spherical shape.

The difference between the ellipsoid of revolution representing the earth and a sphere is very small.

The size is represented by radius at the equator, the semi-major axis and designated by letter, a.

The shape of the ellipsoid is given by the flattening,f which indicates how closely an ellipsoid approaches a spherical shape.

2.2. HEIGHT ABOVE THE AVERAGE SEA LEVEL, ELLIPSOIDAL HEIGHT AND GEODE SEPARATION*

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Ketinggian yang merujuk kepada geoid bagi titik P di atas permukaan topografi dikenali sebagai ketinggian ortometrik, H atau ketinggian Aras Purata Laut (MSL).

Ketinggian ini diukur sepanjang garis pugak antara topografi & geoid melalui ukur aras.

Sementara ketinggian yang merujuk kepada permukaan elipsoid dikenali sebagai ketinggian elipsoid, h.

Ketinggian ini diukur sepanjang garis normal pada ellipsoid daripada cerapan geodesi satelit.

.CONTINUE* Jarak pemisahan di antara permukaan elipsoid dan geoid pula dikenali sebagai ketinggian geoid, N.

Ketinggian Geoid ialah ketinggian di antara permukaan geoid & permukaan elipsoid diukur sepanjang garis normal elipsoid.

Ketinggian ortometrik boleh diterbitkan dari ketinggian elipsoid dan ketinggian geoid dengan menggunakan rumus berikut:

atau

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