Transforming Co-ordinates

(The Transformations module is required for this procedure.)

To transform co-ordinates to a different projection:

  1. Ensure that there is a data base open containing the points that you wish to transform to a different projection.
  2. Select the Transformations task.
  3. Select the Projections/Transform Projection command and use the Transform Projection dialog box to select the projection type and the particular projection to which you wish to transform the co-ordinates. Then select the Transform button to carry out the transformation. Refer to the dialog box help for conditions that the data must meet to perform this type of transformation.
To define a conformal, affine or semi affine transformation and use it to transform co-ordinates:
  1. Ensure that there is a data base open containing the control points on the co-ordinate datum that you wish to transform to.
  2. Select the Transformations task.
  3. Select the Co-ordinates / Define Transformation command and use the Transformation Editor to define the transformation. There are numerous features available in this editor and various procedures that may be used to define the transformation. Refer to the above mentioned help topics for details. The following tips show just one of the methods and do not take advantage of all the editor features.
    Tips:
    • Click in the Control/Point ID fields and use the mouse to select the control points from the graphics window. These define the co-ordinate system that you wish to transform to.
    • If the local points defining the co-ordinate system that you are transforming from are in a different data base, use the Transformations Editor File/Save As command to save the transformation file; then close the editor and open the other data base containing the local points; select Co-ordinates / Define Transformation and then File/open to open the transformation file previously saved.
    • Click in the Local/Point ID fields and use the mouse to select the local points (that correspond to the previously selected control points) from the graphics window. These define the co-ordinate system that you wish to transform from.
    • Use the appropriate Compute (Conformal, Affine, Semi Affine etc.) command to compute the transformation parameters from the co-ordinate pairs. This will define a current transformation. If the Options/Weight menu item is ticked, all co-ordinate pairs must have weights before the parameters can be computed.
    • Use the File/Save command to save the transformations file in case it is needed at a later time to re define the projection. Then close the Transformations Editor.
  4. Select the Co-ordinates / Apply Transformation command to select the points to be transformed and to carry out the transformation.

Note: This procedure described one method of defining a transformation. There are numerous other approaches that can be taken. For example, the control and local points do not need to exist in any data base; they can instead be keyed in from another source.