| Transformations |
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Transformations move data between two different projections.For example, GPS coordinates are in WGS-84 but most GIS data is referenced to another datum such as NAD83, thus the need for a transformation.
Why are datums and moving between them so confusing?Various conventions and lack of standard terms between various software packages makes this topic more challenging than need be. 1. Despite “to" in the name, a transformation such as ‘NAD_1983_to_WGS_1984’ transformation moves data in either direction. This is because the name really referes to the "math" or paramters used to move betwen the two. The software knows which datum it is moving to and from and applies positive or negative values of the numerical parameters accordingly.
2. Sometimes, ‘NAD_1983_to_WGS_1984’ is referred to as ‘WGS_1984_to NAD_1983’ - even though the result is the same as per the above line.
3. As datums are updated, the transforms and software should be updated accordingly. This isn’t always the case.
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