Elastic Adjustment Program:- uses Least Squares Principle and variation of coordinates
technique to adjust a list of coordinates to better fit up to 50 fixed positions
The program can accommodate a 3D model for shift, height, rotation and variable scale.
Preparation is straightforward with a text file of the coordinate listing being edited to
include comparative values for fixed points.
A weighted adjustment is calculated for each unfixed point dependent upon proximity to all
fixed points.
The model produced is contorted with all fixed points remaining with exactly their original
values whilst other points are rubber banded.
Note that the program is not intended as an adjustment for actual observations rather as
post processing to improve the fit.
The program was developed to repair the relationship of the base cadastral plan of Dora
Creek Sewerage Project to the as-constructed survey measurements.
The base plan was a mosaic of manually entered Deposited Plans with errors approaching a
metre(!) over the 20 square km. apparent from closed survey to original survey marks.
By filtering the base plan through this adjustment the survey measurements were not
compromised and the relationship of sewer infrastructure to boundaries was less than 0.2
metres specified by the construction Authority.
As this type of adjustment caters for variable scale within the model rather than producing
an overall best fit the original lot dimensions were essentially preserved within local areas
according to survey marks found.
The program works in conjunction with other CAD software (e.g.CivilCAD, MicroSurvey
etc.) when lines rather than points are to be adjusted. The method in this case requires
points to be permanently attached to all lines. An ascii output of all points from the CAD
software is generated and then filtered through the Elastic Adjustment Program - the
resultant ascii file is then reimported into the CAD software altering the point values and
hence line positions.
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