.. _fieldmaps_page:

Fieldmaps
*********

.. warning::

  Fieldmaps corrections are not yet implemented.

In a nutshell, the information we need to create a VDM in SPM (see ``calculate VDM`` module in SPM batch):

- ``blip direction``
- ``echo time``
- ``total EPI readout time``

Inferring ``blip direction`` and ``echo time`` from a dataset that has sufficient metadata is usually simple.

But ``total EPI readout time`` is not mentioned, so it has to be computed from the information we have,
it is not entirely clear how (see the comments with a lot of ``???`` in ``getTotalReadoutTime``).

Things that are yet unclear:

- is it actually possible to compute total EPI readout time that SPM needs
  from the info in a typical dataset with fieldmaps like ``openneuro/ds001168``?

- If it is not then that is an issue because it means some BIDS dataset are not usable with SPM.

Things to keep an eye on: the code from this `repo <https://github.com/nipreps/sdcflows>`_
from the fMRIprep team could have answers for us.

Functions involved
==================

Workflows
---------

- :func:`bidsCreateVDM`

Batches
-------

- :func:`setBatchCoregistrationFmap`
- :func:`setBatchCreateVDMs`
- :func:`setBatchComputeVDM`

Functions
---------

- :func:`getBlipDirection`
- :func:`getMetadataFromIntendedForFunc`
- :func:`getTotalReadoutTime`
- :func:`getVdmFile`