SGEOID09

There is a degree of difficulty in relating GPS heights obtained from Global Positioning System (GPS) surveying to the existing national leveling networks in most countries where GPS survey is used alongside traditional survey methods. Heights provided by GPS relate to the surface of an ellipsoid, which approximates the shape of the earth, but does not coincide with the geoid. GPS can only be used in most countries to measure the heights meaningfully only above a reference datum if the relationship between the ellipsoid and the geoid is established.

The vertical datum is the reference used for high precision height positioning measurement. To realise this vertical datum, ground points with known height values referenced to the vertical datum are established in many countries.

In Singapore, the official Singapore's vertical reference datum used for cadastral surveys is the Survey Department's datum, which can be referenced using a Singapore's network of control points, individually known as Precise Levelling Benchmarks (PLBMs).

In order to achieve consistency for all height positioning activities on land in Singapore, to be aligned with Survey Department's datum, all levelling surveys should be linked to PLBMs that are aligned to the Survey Department's official datum.

With the increasing use of GPS in positioning activities, it is now possible to obtain surface planar coordinates (X and Y) as well as a GPS height (Z). However, the height coordinate from GPS is referenced to a mathematical model known as an ellipsoid.

Note that a GPS receiver on a ship at sea level (tides not considered) during the course of a long voyage, may indicate height variations, This is because GPS satellites can only measure heights relative to a geocentric reference ellipsoid as they orbit about the center of gravity of the Earth. As a result, GPS height must be corrected to obtain geoidal height while in traditional leveling, the height obtained will always be geoidal height.

A Geoid is a model of the equipotential surface of the earth's gravity field that is best approximated by the mean sea level over the oceans which extends hypothetically beneath all land surfaces (DMA, 1997)

SGEOID09 is the geoid model for Singapore. A good geoid model allows us to determine geoidal heights using Global Positioning System (GPS) (which yields ellipsoid height).

•  Engineering surveys
•  Vertical deformation monitoring
•  Asset Tracking
•  Coastal monitoring

•  Engineering deformation monitoring for reservoir embankment
•  3-dimensional coordinates for stations of the London Water Ring Main project (Dodson, 1995)

Last Update : 01 January 1970