StarNet v6 manual - Engineering Surveyor

Option Group: Local Jobs
Chapter 4 Options
A coordinate datum must be assumed when you are performing a local adjustment so that
adjusted observations are consistent with the given coordinates. Observations will be
reduced to your coordinate datum using one of two methods:
� Apply an Average Scale Factor – If your controlling coordinates are at your default
project elevation, set a factor equal to 1. But if your coordinates are at a different
datum and you know the scale factor (perhaps you are simulating a grid adjustment
and know the average grid factor), enter this scale factor and STAR*NET will apply
it to the horizontal component of all distances during the adjustment to produce
coordinates at your desired datum.
An inline “.SCALE” option may be used to change the default scale factor anywhere
in your data file.
� Reduce to a Common Elevation – Using this alternate scheme, observations at
various elevations are reduced to your given elevation datum using curved-earth
geometry. If the elevation is given as 0.00, horizontal components of distance
observations are reduced to sea level. Therefore controlling coordinates at sea level
must be given as input, and coordinates at sea level will be produced as output.
Likewise, if your given elevation is at some other value, say 1000 feet, the distance
observations will be reduced or expanded to this datum. Coordinates at this datum
must be used as input, and adjusted coordinates at this datum will be produced.
See page 202 in Appendix C for more a detailed explanation of these data schemes.
Option Group: Grid Jobs
For grid adjustments, a value should be given for Average Geoid Height which is the
average geoid-ellipsiod separation for your project. This value is always entered in
meters. Be sure to use the correct sign! For example, the geoid height is negative in the
contiguous United States but may be positive in other areas.
This average geoid-ellipsiod separation is used in the calculation of scale and elevation
factors, and of course, in the determination of ellipsoid height output values calculated
from given or adjusted elevation values, and visa versa.
For the standard STAR*NET edition, the entered geoid height value is used for the entire
project and therefore any deflections of vertical due to gravity variations are assumed to
be zero. But in the “Professional” edition, which includes the handling of GPS vectors,
values for geoid height and vertical deflection may be defined for every point, or they
may be set by geoid and deflection modeling.
See Chapter 10, “Adjustments in Grid Coordinate Systems” for detailed information on
setting options for grid system adjustments
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