The Zone-to-Zone transformation (conversion) is used to convert coordinates between different projection grids defined on the same horizontal datum, for example between a single-zone/special-area project grid and a standard Transverse Mercator grid, or between grids of a different projection type in the same region, for example between a Transverse Mercator grid and an overlapping Lambert's Conformal Conic grid. The process involves conversion of the source grid coordinates into their geographic equivalents, then back again into the grid coordinates for the target projection. There is no actual transformation between different datums, merely a conversion of the coordinates from one zone to the corresponding coordinates in another. In fact when defining a Zone-to-Zone transformation, both datums must be the same.
|IMPORTANT - ALWAYS verify the accuracy and reliability of a transformation before applying to critical data - always test first with points whose coordinates are known in both systems.|
General Transformation Principles
General transformation principles will be found under the main topic for this section, Data Transformations - General.
Zone-to-Zone transformations are defined in the Transformations option under the Zone-to-Zone tab. The datum must be the same for both grids, hence during definition, the To datum will always be automatically set to the same as the currently selected From datum (and cannot be changed), and the zones must be different, either as adjacent and over-lapping zones, or one or both zones may be overlapping special-area project grid zones. One of the following conditions must apply:
Points do not require valid heights as the transformation is applied horizontally only, but existing heights will be retained. The vertical datum should remain the same for this transformation; a different vertical datum may be selected if necessary but is not recommended.
The direction of the transformation is as defined by the Definitions library (in Transformations) but may be applied in the reverse direction if required. Usually, the direction will be determined according to the selected transformation and the grid projection defined for the current job.
Further details of the transformation options will be found in the Transform Job topic.
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