Transformations

In accordance with ISO 19111, there are two types of operations to relate two different CRS: conversion operations and transformation operations:

If a transformation is needed, you must choose the type of transformation for the layer in the CRS selection dialog (see Figure 20) and click the Next button to continue to the corresponding transformation dialog.

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Figure 20: Select the type of transformation

The transformation dialog depends on the type of transformation to be performed:

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Figure 21: Transformación EPSG

Keep in mind that the transformation operations of this type are always between the base CRS (i.e. non-projected CRS), and therefore if the CRS of the view or the CRS of the layer is projected, the corresponding base CRS will appear in the fields Source CRS and Destination CRS. Keep also in mind that for this type of transformation, the CRS for the View and the CRS for the layer must come from the same EPSG repository. If they come from different repositories, the table will appear empty.

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Figure 22: Manual transformation

IMPORTANT: The grid file has a specific scope, which can be deduced from the file information that is displayed in the processing panel. Transformation is not applied beyond this scope, so the re-projection accuracy will be considerably lower, since only the corresponding coordinate system conversion would be applied.

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Figure 23: Grid based transformation

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Figure 24: Selection of the CRS for the layer and recent transformation

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Figure 25: Information of the CRS for the layer and the selected transformation

The second way to select a recent transformation is through the selection of CRS without transformation and then select Recent transformations as the type of transformation, after which a panel is displayed where you can choose from transformations that were previously defined (see Figure 26).

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Figure 26: Recent transformations

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Figure 27: Select the transformation for the CRS of the layer

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Figure 28: Select the transformation for the CRS of the view