Sect_11.2.5

11.2.5 GPS Network Transformations

THE OUTPUT

The results of a transformation adjustment are a set of parameters, and two sets of adjusted coordinates.

The Adjusted Coordinates

The adjusted coordinates of network A have the same weighted scale, orientation and location as their apriori coordinates. Similarly, the adjusted coordinates of network B have the same weighted scale, orientation and location as their apriori coordinates. Thus, the overall scale, location and orientation of each network remains unchanged, only the individual coordinates, angles and lengths change. In other words, the movements of points within a network are small and the overall characteristics of the nets do not change.

Statistical Testing

There are a number of statistical tests that can be applied (HARVEY, 1994), among which are:

Variance factor test.
Tests of parameters, to determine if they are statistically different to zero.
Tests on the residuals, for example to see if they are normally distributed, or to search for outliers.
Tests for regional or local distortions.

The usefulness and reliability of such tests grows with an increase in the "degrees of freedom" of the adjustment (that is, by including more common points). Some tests are based on leaving out certain points, and using these to check the transformation parameter model.

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