Converting items between Coordinate Systems

Use Replicate (Edit > Clipboard) to convert an item into another coordinate system.

This simply copies the selected items from their original datasets to the dataset in the current overlay (provided the current overlay is editable).

The dataset on the current overlay should be set to the desired coordinate system.

We urge caution when converting items between coordinate systems as accuracy is often lost in subtle ways.

For example when a straight LineString item is converted, both endpoints are converted accurately but the LineString item is assumed to be straight in the new coordinate system.

This can cause problems where the new and old coordinate systems are curved relative to each other.

When converting positions between coordinate systems based on ellipsoids (e.g. Transverse Mercator to Latitude/Longitude), the geodetic data of the two coordinate systems are examined.

If the geodetic data is not the same, Cadcorp SIS Desktop will perform a geodetic datum transformation.

• If Cadcorp SIS Desktop recognises the geodetic datum, then regression polynomials are used (which are normally accurate to a few metres in the designed area).
• If Cadcorp SIS Desktop does not recognise the geodetic datum or the position is not inside the designed area, then the seven-parameter Bursa-Wolf method is used.

TIP: For greater accuracy you can set all seven parameters in your area of interest. These parameters are: X, Y and Z shift (in metres), X, Y and Z rotation (in degrees) and a correction (in ppm).

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