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Interpretation of Known Points Test (Global Test)

The Global Test can be performed separately for plan and height, or together in a 3D calculation. You must select the calculation type before starting. The test begins by calculating the error square sum in the established free network, after which all the released points are locked.

Key Values

  • Test Value (Fisher-test): Statistical F-value determined from the probability of error and number of redundancies
  • Calculated: Calculated value based on the difference in error square sums

Info

The Global Test is satisfied if the first value is LESS than the last.

Question

If the Global Test is not OK, what causes the constraint?

  • Is there a general scale error in the network?
  • Are there incorrect coordinates in some of the points?
  • With GPS vectors, the constraint might be due to rotation or vertical deflection

Result Display

The Global Test results can be found in the Summary and in the Global Test report.

Summary of Key Figures

The first part of the summary shows key figures for free and constrained adjustment:

  • Number of redundant obs.:
    Number of observations - (number of unknown elements + number of orientation elements)

  • Number of unknowns:
    Sum of all unknown elements in the adjustment (X, Y, Z and any additional unknowns)

  • Calculated standard deviation of unit weight:
    Estimated standard deviation of the unit weight

  • Sum PVV:
    Weighted error square sum

F-test Values

Following this is an overview of various F-test values as points are released or constrained:

  • F-test requirement:
    Statistical F-value at given probability of error

  • F-test calculated:
    Calculated F-value according to formula

Interpretation of Change Tests

Note

After running the Global Test, you can choose whether to run a test of changes. If you choose to perform the test, you will find the results in the Global Test report.

Example of Reported Results

Global Test, test of changes:

Point Action dX dY dXY Limit dZ Limit
TP105 keep released 0.026 0.013 0.029 0.029 -0.016 0.080
TP118 keep released 0.057 -0.080 0.098 0.046 -0.051 0.140

Info

Points with changes less than the limit value are locked again (0). The other points remain released (1).

Explanation of Values

  • Action:
    Indicates whether the point is locked with original values or remains released with new coordinate values

  • Changes in plan (dX/dY):
    Difference between old and new coordinate values in plan. Coordinate changes are determined with sign - new value minus old

  • Distance (dXY):
    Distance between new and old position. Always given as positive

  • Limit value:
    Determined from the probability of error

  • Changes in height (dZ):
    Difference between old and new coordinate values in height. Change is determined with sign - new value minus old

  • Limit value:
    Determined from the probability of error