Using Transform

This Tech Tip explains how to Apply a Helmert transformation on all or part of the drawing.

Procedure
The Helmert transform requires at least three common points between the old and the new coordinate systems. You may input up to 100 common coordinates.

Modify Menu › Transform




Select which option you require and click on the tick button


Click on the YES button if you want to identify the transformation points graphically. If you would rather type in a list of the transformation points click on the NO button.

Indicate Transformation Points (Yes selected)


Indicate a known point on the old coordinate system.


Indicate the position of the point in the new coordinate system. The CAD will then prompt for the second and third set of coordinates. Thereafter it will ask:


Click on the YES button to continue adding common coordinates. Alternatively click on the NO button to continue to the next step. The Transform Settings dialog will be displayed.


Click on the YES button to continue or the NO button to terminate the function. If you have decided to accept the settings the Transform Parameters will be displayed.


These are the actual parameters which will be applied during the transformation. Click on OK to continue and the drawing will be transformed.

Type in transformation points (No selected)
This option allows you to type in a list of old and new coordinates. The Transform Parameters table will be displayed. Input the coordinate sets as shown below.


You must input a minimum of 3 sets of coordinates. Click on OK to complete the transform or on Cancel to terminate the function.

Clarke to WGS84
A new method of transforming points from Clarke 1880 to WGS 84 has been introduced specifically for South African clients.

This transformation is based on degree squares for which the required transformation parameters have been pre-calculated. These parameters are applied to all points within their containing degree square in order to calculate corrected coordinates.

Modify Menu › Clarke -> WGS84 (SA Only)




Select which option you require and click on the tick button


Specify the central LO


Select the folder where the knb files are stored. The program will then transform the drawing, if the incorrect knb files are selected the following error will appear:


The transformation is dependant on degree square files (KNB files) which can be obtained from the following (sole) supplier:

Mark Newling
Tritan Survey cc
PO Box 18597
Wynberg
7824
Tel: 021 797-2081
Fax: 021 797-8195
EMail: tritansa@iafrica.com


The supply and use of the KNB files supplied by Mark Newling and Tritan Survey is a matter between yourself and their company and Knowledge Base will, other than to the extent of verifying that the internal calculation used is correct, bear no responsibility for the outcome of any transformation using these supplied files

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