Confidence Interval and Uncertainty Display
The Users Options provides a set of controls for both uncertainty computation and reporting purposes on the Analysis tab
The Confidence Interval directly determines the reported uncertainty magnitude values reported for a point. For example, if you use the default 1.0 sigma Confidence Interval then you are making a statement in your report that you have a 68.26% confidence that the true measurement lies within the uncertainty parameters. If you want higher confidence, you can set the uncertainty to 3.0 sigma for example, which will greatly increase the uncertainty magnitudes reported but allow you to state a 99.74% confidence.
Uncertainty can be displayed wither using a Monte Carlo simulation process that generates an uncertainty cloud or can be performed using a Covariance analysis.
For uncertainty cloud display :
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The number of Sensitivity Samples used in this calculation can also be adjusted. The default is 1000. Increasing the number of samples give you a better estimate but will also take more time to compute. Reducing the number will accelerate the process but cause outliers to have a greater influence on the results.
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A check box is also available to Draw Using Lines which converts the way a cloud is displayed from a set of cloud points (that can be hard to see), to a set of lines drawn from the center to each cloud point in the uncertainty cloud.
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When the Apply Gaussian dist. option is enabled, point coordinates values are perturbed using a Gaussian random number generator (utilizing a Box-Muller algorithm) to build a new point coordinate, injecting random error into each of these instrument variables.
Sensitivity clouds are handled differently than other point clouds. For this reason we have a separate Cloud Magnification value which helps visualize these clouds graphically. Increasing the magnification value will scale the cloud about the measurement to make it easier to see. The deviations can also be depicted as lines drawn from the measured point. This magnification control also controls the size of uncertainty ellipsoids when enabled.
Uncertainty can also be performed using Covariance analysis. Because it does not use a simulation process for the computation it is both faster and does not produce uncertainty clouds. As an alternative, ellipsoids can be displayed to encompass the region of uncertainty.
For uncertainty ellipsoid display :
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Draw Uncertainty Ellipsoids. This option enables ellipsoid display over uncertainty cloud display. Uncertainty ellipsoids can be displayed either With Respect To (WRT) the Instrument Base or the WORLD frame. The ellipsoid display can be toggled from solid to wire frame using the option Alignment>Network Alignments>Coordinate Uncertainty>Toggle Wireframe Uncertainty Ellipse (Ctr+Alt+W)
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WRT Instrument Base. Uncertainty ellipsoids can be displayed either With Respect To (WRT) the Instrument Base or the WORLD frame. When the instrument base is selected the resulting uncertainty ellipsoids will be displayed the error in the points generated from that instrument, excluding any additional instrument position error.
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WRT WORLD. Choosing to display ellipsoids With Respect To (WRT) the WOLRD frame will combine both the instrument base uncertainty (if available from a an alignment) with the point uncertainty.
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