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Geomatics for Air Navigation

C04: Datum definition. Horizontal and vertical datums. Coordinate transformations.

Eng. Tiberius TOMOIAGĂ, PhDPhone: 0722.91.46.22Email: [email protected]

Revenge of the Shift

Ellipsoid

3D Coordinate System

What's a Datum? Prior to satellite mapping technology, the

best approximation of the shape of theearth was the geoid, which evolved intoslightly flattened spheroids or ellipsoids.

Geographic coordinate systems use aspheroid to calculate positions on theearth.

Datum definition Geodetic datums define the size and

shape of the earth and the origin andorientation of the coordinate systems usedto map the earth.

A datum defines the position of thespheroid relative to the center of the earth.

The origin of the WGS84 ellipsoid is at the Earth’s center of mass, which makes it ideal for a GPS datum

Datum definition

Datum definition

Datum Origin on Surface of Earth

Ellipsoid Model based on less precise surveys

Datum definition

Datum shift

Common Datum Shift Parameters

Common Datum Shift Parameters

Common Datum Shift Parameters

Common Datum Shift Parameters

Common Datum Shift Parameters

Common Datum Shift Parameters

European vertical datums

17

ellipsoid

geoid

N

Vertical datum

Importance of datums

Importance of datums

Coordinate transformation

Coordinate transformation

Coordinate transformation

Coordinate transformation

Coordinate transformation

Where:- ∆X, ∆Y, ∆ Z – translations (shifts)- rx, ry, rz – rotations- s - scale factor

Coordinate transformation

Coordinate transformation

Coordinate transformation

20 0 0cos cos cos sin sin sini i i i i i iN a X Y Z a fϕ λ ϕ λ ϕ ϕ∆ = ∆ + ∆ + ∆ + ∆ + ∆

Vertical datum transformation: geoidheight differences between differentdatums (e.g. WGS84 and PZ90).

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