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STAR*NET V6 - Circe

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Chapter 8 Analysis of Adjustment Output<br />

The next section shows the error ellipses and elevation confidences computed using the<br />

confidence level you chose in the project options. The error ellipse parameters define the<br />

shape and size of the confidence region around each station. In the output below, for<br />

example, you can say with 95% certainty the adjusted station lies somewhere within the<br />

ellipse region.<br />

Station Coordinate Error Ellipses (FeetUS)<br />

Confidence Region = 95%<br />

Station Semi-Major Semi-Minor Azimuth of Elev<br />

Axis Axis Major Axis<br />

1 0.00000 0.00000 0-00 0.00000<br />

2 0.05980 0.04579 29-17 0.07472<br />

3 0.06722 0.05219 159-23 0.07510<br />

Station Error Ellipses (3D Example)<br />

If the adjustment passes the Chi Square test, the adjusted coordinate standard deviations<br />

are used to compute the error ellipses directly. However, if the adjustment fails the Chi<br />

Square test, the standard deviations are increased by the computed Total Error Factor, to<br />

reflect the weak adjustment. This is done to protect you from generating artificially small<br />

ellipses by reducing your global observation standard errors to the point where the<br />

adjustment is no longer valid.<br />

The last section resulting from error propagation shows relative ellipses and a vertical<br />

difference confidence. By default, relative error ellipse information is computed between<br />

each station connected by an observation. Alternately, the “.RELATIVE” inline options<br />

can be used to control exactly which ellipses to compute. Relative ellipses provide an<br />

estimate of the accuracy of the relative positions of two stations. Two stations can have<br />

large error ellipses but a small relative ellipse between them, if their positions are highly<br />

correlated. Note that relative ellipses are also inflated by the Total Error Factor if the<br />

adjustment fails the Chi Square test. For detailed information on ellipse and relative<br />

ellipse interpretation see the next section.<br />

Relative Error Ellipses<br />

Confidence Region = 95%<br />

Stations Semi-Major Semi-Minor Azimuth of Vertical<br />

From To Axis Axis Major Axis<br />

2 13 0.06135 0.03833 63-47 0.06248<br />

4 15 0.07709 0.05626 54-01 0.09281<br />

2 19 0.07856 0.06761 170-50 0.04554<br />

Relative Error Ellipses (3D Example)<br />

131

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