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Konsep Dasar Geodesi

Disamping pengetahuan dasar tentang penentuan posisi horizontal dan vertikal dengan cara konvensional maupun GPS beberapaistilah2 dasar yang mendominasi didalam dunia survai dan pemetaan.

• Geoid• Ellipsoid• Undulasi• System Proyeksi Peta• Transformasi Datum

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Geoid

Geoid ModelGeoid Model

Scaled15 000 timesScaled15 000 times

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Geoid

• Equipotential surface / field gravity surface or « zero surface »

• Corresponds approximately to mean sea level, continued under continents.

• Irregular and multiple undulations.

• No analytical definition.

• It has a physical reality but bad geometric definition.

• Models performed by astro-geodesic and gravimetric measurements.

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Ellipsoid

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System Tinggi

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Helmert's Projection

•N is the Geoid-Ellipsoid Separation. •H is the Orthometric Height. •h is the Ellipsoidal Height.. •P is the angle between vertical and the normal to the ellipsoid. •Strictly speaking:

h = N + H cos(P)

Because P is very close to zero, cos(P) is so close to 1.0 that the difference is negligible. Hence

h = N + H

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Referensi Tinggi

• MSL elevation is roughly equivalent to orthometric height (H), the technical name for height above the geoid.

• Geoid height (N) is the separation between the geoid and the ellipsoid. It can be plus or minus.

• Ellipsoid height (h) is the distance above or below the ellipsoid (plus or minus). Ellipsoid height is also called geodetic height

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Korelasi antara Geoid, Ellipsoid Local dan Ellipsoid Global

n

nvgeoid

local ellipsoid

n : normal to ellipsoidn : normal to ellipsoid

v : vertical ( geoid)v : vertical ( geoid)

global ellipsoidglobal ellipsoid

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Map Projection

Projection: The Big Slide ShowMap projection is the process through which the curved surface of the earth is represented on a flat piece of paper. This process can be thought of as a slide show where: •The light source is at the center of the earth. •The surface of the earth is the slide. •The screen is the map.

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Projeksi Peta

Projeksi Mercator

Normal Transverse Oblique

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Projeksi Peta

Projeksi Kerucut

Normal Oblique

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Projeksi Peta

Projeksi Plane

Polar Oblique Equatorial

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Projeksi Peta

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Projeksi Peta

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DATUM

• What is a datum?A datum is a point, a line, or surface used as a reference in surveying and mapping. A geodetic datum is a mathematical model of the earth used to calculate the coordinates on any map.

• Why is it important?The main problem oil and gas industry working in many coutries use their own datum when making their maps and doing their survey. These are referred to as local datums. The same area may have two datums giving each point two different coordinates. In addition datums generated by individual countries do not match at their boundaries.

• Transformation Parameters

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Datum Shift

CARTO. / GEOG.CARTO. / GEOG.Projection 1Projection 1Ellipsoid 1Ellipsoid 1

GEOG. / GEOC.GEOG. / GEOC.Ellipsoid 1Ellipsoid 1

DATUM 1DATUM 1

GEOG. / CARTO. GEOG. / CARTO. Projection 2Projection 2Ellipsoid 2Ellipsoid 2

GEOC. / GEOG. GEOC. / GEOG. Ellipsoid 2Ellipsoid 2

DATUM 2DATUM 2

E2, N2E2, N22, 2, 22

X2X2

Y2Y2

Z2Z2

DATUM DATUM SHIFTSHIFT

dX, dY, dZROT X,Y,ZScale factor