This topic documents the concept of projections.
When a new data base is created using the Utilities/File/New command, it may be specified as being on a plane or alternatively as being on a projection.
The following projection types are available.
- Plane (Plane geometry; no projection)
- Transverse Mercator (Includes UTM)
- Lambert Conformal Conic
- Double Stereographic
- Oblique Mercator
- NAD27 Transverse Mercator
- NAD27 Lambert Conformal Conic
- Swiss
- New Zealand
If the data base is on a plane, then all computations are based on plane trigonometry. Plane directions and grid co-ordinates will be assumed for all input and output. Distances may however be plane or ground values. Refer to the Utilities/Configure/Earth Constants command for an explanation of the difference between plane and ground distances.
If a projection is specified, then all computations are carried out based on that projection. Directions may then be input or output as plane, grid or azimuth. Distances may be plane, ground or ellipsoidal. Co-ordinates may be grid or geographical.
These selections are made in the Utilities/Configure/Units command and can be changed at any time.
Consequently, the data entry fields in the creation dialog boxes are labelled according to the units configuration settings. For example, if distances are set to ellipsoidal, you must be sure to enter an ellipsoidal distance in any distance edit fields.
Note that the projection of a data base cannot be changed after it is created. It is therefore imperative that you create the data base on the required projection with the required projection parameters.
See Also