Sarawak Geodetic Report
A Proposal for geodetic datum development
1.0 Introduction
A national geodetic datum provides a country with a local implementation of global coordinate systems. It minimizes the risk of having different and inconsistent coordinate reference systems. It enables a wide range of spatial applications to be supported in a manner that is consistent with international standards and best practice.
When Borneo Triangulation 1968 (BT68) was established, it complied with the then current recommendations of the International Association of Geodesy (IAG). It used what could be called the global positioning system of the day - geodetic astronomy - to establish the datum origin and orientation As much as the technology of the day allowed, it was an effective implementation of an internationally accepted terrestrial reference system.
Although we now know the difference between the centre of the BT68 ellipsoid and the centre of mass of the earth, until the advent of satellite geodesy in the 1960’s and 1970’s, this difference was not really measurable and was therefore of no practical consequence. The same is true of many other national datums around the world that were developed around this time.
It was only in the late 1980’s and 1990’s that an increasingly used satellite based geodetic measuring system - the Global Positioning System (GPS) - began to impact on the utility of the national datums of many countries. The inconsistency between BT68 and international reference systems started to impact adversely on navigation, scientific applications and on routine spatial data management.
Prior to this, internal distortions of the datum due to earth deformation also began to impact on geodetic processing. The introduction of EDM highlighted variations in the definition of scale and the new observations were inconsistent with the distances derived from coordinates of geodetic stations. GPS, with its potential to efficiently meet existing survey accuracy requirements over
1.0 Introduction
A national geodetic datum provides a country with a local implementation of global coordinate systems. It minimizes the risk of having different and inconsistent coordinate reference systems. It enables a wide range of spatial applications to be supported in a manner that is consistent with international standards and best practice.
When Borneo Triangulation 1968 (BT68) was established, it complied with the then current recommendations of the International Association of Geodesy (IAG). It used what could be called the global positioning system of the day - geodetic astronomy - to establish the datum origin and orientation As much as the technology of the day allowed, it was an effective implementation of an internationally accepted terrestrial reference system.
Although we now know the difference between the centre of the BT68 ellipsoid and the centre of mass of the earth, until the advent of satellite geodesy in the 1960’s and 1970’s, this difference was not really measurable and was therefore of no practical consequence. The same is true of many other national datums around the world that were developed around this time.
It was only in the late 1980’s and 1990’s that an increasingly used satellite based geodetic measuring system - the Global Positioning System (GPS) - began to impact on the utility of the national datums of many countries. The inconsistency between BT68 and international reference systems started to impact adversely on navigation, scientific applications and on routine spatial data management.
Prior to this, internal distortions of the datum due to earth deformation also began to impact on geodetic processing. The introduction of EDM highlighted variations in the definition of scale and the new observations were inconsistent with the distances derived from coordinates of geodetic stations. GPS, with its potential to efficiently meet existing survey accuracy requirements over