The pyAFQ Mapping API
~~~~~~~~~~~~~~~~~~~~~~

pyAFQ has a system for users to specify how to register an image from each
subject to a given template, called the mapping. The mapping API is similar
to our Mask API.

In the :mod:`AFQ.definitions.mapping` module, there are four mapping classes
one can use to specify the mapping. As a user, one should initialize mapping
classes and pass them to the AFQ.api objects, or write out the initialization
as a string inside of one's configuration file for use with the CLI.

- :class:`AFQ.definitions.mapping.SynMap`: The default mapping class is to
  use Symmetric Diffeomorphic Image Registration (SyN). This is done with an
  optional linear pre-alignment by default. The parameters of the pre-alginment
  can be specified when initializing the SynMap.

- :class:`AFQ.definitions.mapping.SlrMap`: Use this class to tell pyAFQ to use
  Streamline-based Linear Registration (SLR) for registration. Note that the
  reg_template and reg_subject parameters passed to :class:`AFQ.api.group.GroupAFQ` should
  be streamlines when using this registration.

- :class:`AFQ.definitions.mapping.AffMap`: This will only perform a linear
  alignment for registration.

- :class:`AFQ.definitions.mapping.FnirtMap`: If you have an existing mapping
  calculated using Fnirt, you can pass bids filters to :class:`AFQ.definitions.mapping.FnirtMap`
  and pyAFQ will find and use that mapping.