Differences in functionality between the Native and Shared interfaces

The Shared API is meant to abstract out the details of the WCS implementation and provide a uniform way to evaluate the transforms regardless of the underlying implementations in different WCS packages. As such it is the “lowest common denominator” of the existing WCS libraries that support it, currently astropy.wcs and gwcs.

Because GWCS aims to be flexible and general, there is functionality that can only be achieved with the Native Interface. Some of the differences are listed below:

• The Shared Interface methods call under the hood the Native methods with their default options. One of the consequences is that the transform evaluation happens always within the bounding_box of the WCS and values outside it are set to np.nan.

• The Shared Interface methods work only on the total transform while GWCS can execute transforms between intermediate frames.

• Since the Shared Interface methods do not accept keyword arguments, if the numerical_inverse method is invoked, it runs with default parameters.