KNB Clarke to WGS84

Apply a KNB transformation to the drawing.

This function allows you to convert drawing entities from the Clarke 1880 mapping datum to WGS84, using commercially available KNB files. The drawing entities are modified in position to reflect the transformation.

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. Other than verifying that the internal calculation used is correct, Knowledge Base bears no responsibility for the outcome of any transformation using these supplied files.

Procedure

1. You are asked:

• All - All the points, lines and polylines/polygons in the drawing will be exported.

• Visible - Only the visible points, lines and polylines/polygons in the drawing will be exported.

• Selected - Only the selected points, lines and polylines/polygons in the drawing will be exported.

2. Select the option you require and click Enter .

3. You are prompted to:

4. Enter the central longitude (prime meridian) that this survey drawing references. This is very important as the required KNB file for this area of South Africa depends on the central longitude.

5. The file browser displays. Select the directory in which your KNB files are stored.

6. Click OK to continue or Cancel to terminate the function.

7. If the correct degree square files are found, the calculation continues and the entities are transformed.

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.