Resection recorder data

Global variance factor (GVF) displays a number, which is the F test statistic divided by the redundancy. This GVF test applies to all observations and accuracies in the resection. It tests how well the observations align with the expected variations calculated from the accuracy of the instrument. One of several possible messages are displayed below GVF. The following list shows a recommended action to take for each message.

• Within acceptable limits.

The accuracies set are appropriate for the observations, and the GVF and the Pope’s Tau tests pass at the confidence level you have chosen. No outliers are found. Check that the Confidence level is appropriate (typically 0.9 or 0.95). If it is, then no action is needed.

• Accuracy parameters too low.

The observations are unexpectedly accurate. Edit the values on the Accuracies tab to indicate that the measuring equipment was more accurate.

• Within acceptable limits.

The values in the accuracies tab are appropriate for the observations at the selected Confidence level. You can proceed to examine the Pope’s Tau test values for outliers.

• Observations may contain outliers.

Potential outliers are marked in red. The Pope’s Tau test is an iterative data-investigation method. Clear the check box for the observation with the bold red Tau value. Then re-examine the results and remove another observation if needed.

• Not enough observation data.

There are not enough observations available to calculate the Global variance factor. This could be because there are not enough observations in the code block, or because you have cleared too many observations. Turn on more observations if possible.

Typically, you would use a confidence level of 0.95. 0.90 gives the most robust confidence and 0.99 the least robust confidence.

• Selected: The row of observations is used to calculate the position of the resected point.
• Cleared: The row of observations is not used.

Note: You can also include or exclude individual parts of an observation (Hz Angle, Vert Angle, Slope Dist) by selecting or clearing the check box beside that part.

The instrument (as defined in the station errors table) used for the calculations. This field is selectable if all of the following are true:

• A station errors table exists in the survey database
• Multiple instruments have been defined in the station errors table (that is, there is a choice of instruments).
• The new station has not been created using only one horizontal angle, one vertical angle, and one slope distance observation

Read-only. This field is used in conjunction with the station errors table, which is an optional table in the survey database used to set up a QA regime for new stations entering the survey database. The values for this field depend on whether the station errors table has been created, and is being used.

• If you are using the station errors table, this field contains an identifier that represents the order or 'quality' of a station, for example 1st, 2nd or 3rd.
• If you have not created a station errors table this field is empty.
• If you have created a station errors table, any station that is used as a fixed station (for example, as a backsight station) in the creation of a new station in the database has the value that has been defined in the station errors table.