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When to use ArcMap for a geographic transformation?
When working with geographic transformations, if no mention is made of the direction, an application or tool like ArcMap will handle the directionality automatically. For example, if converting data from WGS 1984 to NAD 1927, you can pick a transformation called NAD_1927_to_WGS_1984_3 and the software will apply it correctly.
Can a geographic ( datum ) transformation be automatically applied?
The geographic (datum) transformation cannot be automatically applied because many geographic coordinate systems and transformations exist for a given area. Geographic transformations use different methods, with different accuracies, and are defined for particular areas.
What does a larger number mean in ArcMap?
This number represents the order in which the transformations were defined. A larger number does not necessarily mean a more accurate transformation. Even though a geographic transformation has a built-in directionality, all transformation methods are inversible. That is, a transformation can be used in either direction.
What is the accuracy of a geographic transformation?
The accuracy of a particular transformation can range from centimeters to meters depending on the method and the quality and number of control points available to define the transformation parameters. A geographic transformation is always defined in a particular direction.
Can a transform be chosen by default in ArcGIS?
Usually, any transform that you would choose in ArcGIS is precise enough for common mapping needs, but ArcGIS is not transforming datums by default in case of projection. Transformation parameters are the source of discrepancy. Make sure you use the same parameters while transforming back and forth.
How is an affine transformation used in ArcGIS?
An affine transformation can differentially scale the data, skew it, rotate it, and translate it. The graphic below illustrates the four possible changes. where x and y are coordinates of the input layer and x’ and y’ are the transformed coordinates.
How to create a geographic transformation list in ESRI?
Note : The data projection must be defined using an Esri PRJ file in the coordinate system the data is projected to. If the current projection file is human-readable, open the file in Notepad, and compare the parameters with available projection files for that geographic area provided in Esri software.