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ListTransformations

Summary

Returns a list of valid transformation methods. An extent can be used to narrow the list of valid transformation methods for a specific geographic area.

The most appropriate transformation is usually the first one in the returned list. The list is sorted by amount of overlap of the data versus the areas of use of the transformations. If two or more transformations have the same amount of overlap with the data, the transformation accuracy values are used as a secondary sort parameter.

Learn more about geographic datum transformations

Syntax

ListTransformations(from_sr, to_sr, {extent}, {vertical}, {first_only})

Parameter Explanation Data Type

from_sr

The starting geographic coordinate system. This can be specified with a SpatialReference object, the name of the spatial reference, or a path to a projection file (.prj).

SpatialReference

to_sr

The final geographic coordinate system. This can be specified with a SpatialReference object, the name of the spatial reference, or a path to a projection file (.prj).

SpatialReference

extent

Only transformations that span the entire extent will be returned. The extent needs to be specified in coordinates from the from_sr. When working with data, the extent on a Describe object can be used.

Extent

vertical

Specifies whether to return a list of vertical or horizontal transformations. By default, the function returns transformations that ignore vertical coordinate systems on the from_sr and to_sr.

The function returns only one type of transformation. If set to False, horizontal transformations will be returned; if set to True, vertical transformations will be returned.

To use True, both the from_sr and to_sr arguments must have a vertical coordinate system.

To use a transformation result as input to the Project tool, the tool's vertical parameter must be set appropriately to NO_VERTICAL or VERTICAL to match the transformation.

The default value is False.

Boolean

first_only

Specifies whether to limit the list of transformations to a single item or return all valid transformations. This is a performance optimization.

The default value is False.

Boolean

Return value

Data Type Explanation

String

A list of valid transformation methods as strings.

Code sample

ListTransformations example

Use the ListTransformations function to identify valid transformations for projecting from one coordinate system to another.

import arcpy

from_sr = arcpy.SpatialReference('WGS 1984')
to_sr = arcpy.SpatialReference('NAD 1927 StatePlane California VI FIPS 0406')

extent = arcpy.Extent(-178.217598182, 18.9217863640001,
                      -66.969270909, 71.4062354550001)
transformations = arcpy.ListTransformations(from_sr, to_sr, extent)