Search TipsCustomising Coordinate Reference System
A Coordinate Reference System is a method of projecting positions in the world onto screen/paper.
SIS Desktop 9.1 lets you create Coordinate Reference System objects and save them in Named Object Libraries using names.
Click the CRS icon on the status bar to see available coordinate systems.
Alternatively select a. Overlays > Dataset > Coordinates and click b. Edit to open customisation options.
1. Origin
| Latitude | The latitude of the origin of the coordinate reference system. | |
| Longitude | The longitude of the origin of the coordinate reference system. | |
| Prime Meridian | Prime Meridian that the coordinate reference system is based on, relative to Greenwich. A list of Standard Prime Meridians is shown. | |
2. Geodetic Datum
A Geodetic Datum (sometimes called simply a Datum) models the sea-level surface more accurately than an ellipsoid.
SIS Desktop 9.1 contains equations for transforming points between Geodetic Datums or you can make your own Geodetic Datums by applying seven conversion parameters to the WGS84 standard Geodetic Datum.
| Ellipsoid Name | Reference ellipsoid name, i.e. Airy 1830 in this example. | |
| Semi-major axis | Distance from centre of ellipsoid to any point on the equator in metres. | |
| Semi-minor axis | Distance from centre of ellipsoid to either pole in metres. | |
| Inverse flattening (derived) | Inverse flattening value. | |
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WGS84 conversion parameters Translation (m) X/Y/Z |
The difference between the X/Y/Z values of a point in the target and source coordinate reference systems. |
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| Rotation (") |
The angular difference (about the X, Y or Z axis, viewed from the origin) between the other two axes directions of target and source coordinate reference systems. |
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| Scale difference (parts per million) | The scale difference increased by unity equals the ratio of the length of an arbitrary distance between two points in target and source coordinate reference systems. | |
Use the Change WGS84 conversion parameters... button to see and edit the various conversion parameter variants.
3. Properties
Use the Properties tabto edit all relevant properties of the coordinate reference system.
