STAR*NET V6 - Circe

Chapter 5 Preparing Input Data
In general, you should always use standard errors, global project defaults or otherwise,
that reflect the conditions and equipment used to collect your field data. If you believe,
for example, that your angles are “good” to within plus or minus 4 seconds, then do not
use a standard error of 2 seconds to get a “better” adjustment. It will not help. You will
likely get a Total Error Factor in your adjustment statistics that is very different than 1.0,
and the adjustment will fail the Chi Square test.
Except for direction sets, STAR*NET assumes that all input observations are
uncorrelated. This means, for example, that there is no interdependence between two
distance measurements or between angular and distance observations. Note that the
output coordinates from the program will almost certainly have correlation between their
Northing and Easting coordinates. Refer to the section “Ellipse Interpretation,” in
Chapter 8, “Analysis of Adjustment Output” for further information on output coordinate
correlation.
Why do I want to use weights?
Independent weights assigned to observations allow STAR*NET to solve the survey
network more rigorously. Less precise measurements (larger standard errors, smaller
weights) will have less of an influence on the solution, while more precise values
(smaller standard errors, larger weights) will have more of an impact. For example, if
you are combining some old survey data using taped measurements with a new survey
using modern EDM measurements, you may want to give the taped distances higher
standard errors (lower weight) than the EDM measurements.
In order to introduce constraints into a network, it becomes possible to fix an observation
by giving it a very high weight (very small standard error). For example, you may wish to
have a certain azimuth along a line - simply fix the input value with a small standard
error by using the “!” symbol. Conversely, some input values may be only
approximations that you would like not to influence the adjustment. They can be left free
by giving them low weights (high standard errors) with the “*” symbol.
STAR*NET has two special codes (“!” and “*”) to allow you to indicate fixed and free
observations, in order to simplify data input. You should normally use these special
codes rather than creating your own very low or very large standard error values to fix or
free observations.
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