The InfoMate Geodetic Datum Transformer is a complete tool to convert survey co-ordinates and GIS data from Cape datum (or BTRS) to Hartebeesthoek94 datum (or BNGRS02) and vice versa.
The converter uses a Helmert transformation and for applications requiring greater accuracy, an optional weighted mean adjustment. Just submit the file and the converter takes over, providing accurate, topological data.
Control data can be obtained from the NGI (Chief Directorate: Surveys and Mapping). This control data is supplied as files which can be imported into the software. Control data can also be imported from various other formats. For users that do not require centimeter accuracy (for South Africa only), degree square parameters, as supplied by the Chief Directorate: Surveys and Mapping, are built into the software.
- Rigorous For Land Surveyors and other users requiring high accuracy, this conversion uses a rigorous procedure that is designed in accordance with guidelines established by the Surveyor-Generals office in KZN;
- Topological The ability to support topological data formats provides GIS practitioners with the tools to easily convert large GIS databases, whilst retaining topology.
The following input and output formats are supported:
- InfoMate projects;
- ESRI Shapefiles (point, line and polygon features);
- ASCII co-ordinates in various formats;
- Compuplot Cadastral.crd files.
The transformer uses a Helmert transformation to convert the coordinates from the source to the target datum. If the user selects to use the control coordinate data, then either:
- Control Coordinate Transformation: This option calculates the Helmert transformation parameters once and applies the same parameters to all the source coordinates. or;
- Control Coordinate Transformation (per point): This option re-calculates the Helmert transformation parameters for each source coordinate and applies them to that point.
- User defined Helmert transformation: This option applies user definable transformation parameters that can be entered.
In addition, the geographical extent of the transformation can be managed or limited for high end users, such as Land Surveyors and Engineers, where transformation accuracy is of paramount importance. Low accuracy GIS applications may however not require this accuracy and parameters covering larger areas may be acceptable.
If distance weighting is applied, a 1/distance3 adjustment is applied to the final transformed coordinates that effectively favours the closest control point. This strategy was devised by the Surveyor-General in South Africa to obviate the requirement to re-survey beacons that differ by more than 100mm from the existing survey records, thus necesistating the resurvey of these points.