Scale Factor
The projection of the spheroid onto a plane requires that measured distances be adjusted by a scale factor the value of which is determined by the map projection being used. The default scale factor may be changed by this function if you wish to use a more precise scale factor rather than a mean scale factor for the area of interest.
To run this function: Choose Survey > Survey database > Administration > Scale factor, or...
For relatively small areas (Easting dimension < 1000m) a mean scale factor may be used with little in the way of significant errors introduced into the calculation of coordinates. The discrepancy introduced due to the use of a mean scale factor over an area extending 1000m in the East-West direction is approximately +/- 0.0015m.
A default scale factor may be defined in the SSI_ETC:defaults.ssi file. If this scale factor is not defined it is assumed to have a value of 1.0 thus resulting in no adjustments to surveyed distances.
All surveyed distances are multiplied by the scale factor to adjust them to the plane in use by the map projection. The functions where this occurs are:
- Surface Traverse
- Underground Traverse
- EDM Survey
- Generating Distance Stadia Survey
- RDS Survey
- Two-Wires Stadia Survey
- Chain & Offset Survey
- Profile Survey
- Radiation Survey
- All data records
The creation of setout notes requires that the calculated distances between two points must be divided by the scale factor so that the plane distances from the map projection are adjusted to suit the curvature of the Earth and thus ensure that the setouts are in the correct position. Functions where the calculated distances are divided by the scale factor prior to inclusion in a report are:
- Setout Notes
- Grade Line Setout
- Chainage and Offset Setout
Scale factor
The default value, as defined in the SSI_ETC:defaults.ssi file is displayed. Enter the new value for the scale factor and choose Apply. Choose Cancel if you do not wish to change the scale factor.
Note:This does not change the default scale factor defined in the SSI_ETC:defaults.ssi file.