STAR*NET V6 - Circe

Chapter 8 Analysis of Adjustment Output
8.17 Locating the Source of Errors
If the adjustment fails the Chi Square test, there is probably something wrong with the
network configuration, the actual observations, or the weighting. The following
suggestions are designed to help you locate and correct errors in your input data.
Some of the major causes of completely failed or poor adjustments are as follows:
1. Incorrect data entry into STAR*NET - digits transposed, station names wrongly
entered, typing errors in controlling coordinate values, etc.
2. Options set incorrectly such as angle station order set to “At-From-To” but should be
set to “From-At-To”, or visa versa. or other options such as project units, refraction
constant, etc., set improperly for your job.
3. For grid jobs, the zone set incorrectly or geoid height not entered properly.
4. Field data collection blunders - wrong stations observed, station names incorrectly
entered, etc.
5. Incorrect assignment of standard errors to field observations. For example, assigning
small standard error to angles on short sights, but with no centering error value
entered in the Project Options/Instrument settings.
6. Systematic errors in field data - EDM out of calibration, etc.
7. Invalid geometry of the network - fixed azimuth between fixed stations, 3D point
with no vertical observation, etc. STAR*NET attempts to detect these conditions,
but some may get by and cause problems.
8. Weak network geometry - poor intersection angles, lack of redundancy, etc.
Here are some of the symptoms of a poor adjustment. Frequently, many or all of these
symptoms are seen together:
1. Adjustment fails the Chi Square test.
2. Adjustment does not converge within 5 to 10 iterations.
3. Large residuals on observations.
4. Warning messages about Singularities and Geometric Weakness in the solution.
5. Extremely large error ellipses on adjusted points.
6. Fixed stations are showing coordinate changes.
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