GeoIWST 

IWST is short for Iterative Weighted Similarity Transformation and is a new tool available in GeoLab for performing an adjustment primarily used for determining the deformation of stations over time.

This adjustment will remove the datum defects from the station deformations, providing a clearer picture of how a network is actually deforming versus what is measured, providing better insights into the instability of network stations.

Inputs:

These two files must contain the same collection of stations in the same datum (eg. XYZ and XYZ), with a statistically significant period of time having passed between them.

The easiest way to obtain these files is from a GeoLab adjusted network.

Outputs:

  • 3DC group containing the adjusted locations of the deformed stations, with the effects of datum defects removed

  • Final station displacements after weighted transformation (IWST), with datum defects removed

  • Station error ellipses and error ellipsoids

  • Ratio of station displacements to confidence regions

The outputs of IWST can be used to refine the observed locations of unstable stations and make insights as to which observations in the adjustment (for example, those connected to unstable stations) should be assigned less weight.

Loading Input Data

  • Input File: Initial State: paste a file link or click the [...] button to load a file containing a collection of stations and their corresponding varaince/covariance matrix, otherwise known as a 3DD Group.
    This can be generated easily from an existing adjustment file using the Extract Obs... tool.
    Note: when performing an IWST adjustment, both coordinates and variance/covariance data are needed

  • Input File: Secondary State: paste a file link or click the [...] button to load a file containing the same collection of stations as above at a later observation time than the first, over a period of time in which deformation of the stations may have occurred.
    Note: these stations must have the same names and be contained in the same format (eg. PLH and PLH) in both files

  • Output File: paste a link or use the [...] button to select a filepath (file will be overwritten if it already exists) for the IWST output.
    The output will also be displayed on the screen once the adjustment is complete

Performing the Adjustment

  • Confidence Level: select the confidence level for statistical computations of error ellipses and ellipsoids

  • Maximum Number of Iterations: the maximum number of iterations the adjustment process will go through in attempting to bring misclosures below the convergence criterion

  • Convergence Criterion: the maximum acceptable value of any of the misclosures in the adjustment (error representing difference between adjusted value and "real" value of station positions at each iteration).
    The smaller the convergence criterion, the more accurate the adjustment. A convergence criterion of 0.001m will bring all errors to below 1mm within the adjustment and is a normal value.
    Note: if the adjustment will not converge, increase the convergence criterion and the maximum iterations

  • Datum Defects: Number of datum defects, and by effect the style of deformation that is being accounted for in the IWST adjustment.
    Datum defects must match the dimensions of the input points (eg. 2D datum defects with 2D stations).
    Accounting for different datum defects will allow for computation of different movements of deformation, varying across rotations, scales, and transformations

  • Go: perform the IWST adjustment with the given settings.
    This will display the results over the Options menu, which can be closed with the "Done Viewing" button, and print the results to the given Output file

  • Messages: shows any error messages or notifications occuring throughout the adjustment