SpineData from Multi-Label
==========================

Summary
-------
Converts a labeled segmentation volume (multi-label) into a structured ``SpineData`` object that downstream Spine algorithms can use. Use this when you have a spine label map from an external segmentation pipeline and need a ``SpineData`` with vertebrae, sacrum, and ilium for registration or analysis.

See also: :doc:`SpineData <../SpineData>`.

Input
-----
- A single or multi-label 3D label map volume.
- Each vertebra should be its own label value (instance segmentation): one integer id per vertebra region. Non-vertebra labels (e.g., sacrum/ilium) should not be present.

Output
------
- A ``SpineData`` instance containing anatomical structures reconstructed from the label map.
- Structures typically include vertebrae (with per-vertebra geometry), sacrum, and ilium where labeled.

Workflow
--------
1) Load or select your labeled volume.
2) Run “SpineData from Multi-Label”.
3) Inspect the generated ``SpineData`` in 3D; verify vertebra counts and positions.
4) Use the ``SpineData`` as input to downstream altorithms such as registration or analysis (e.g., Poly Rigid Registration, Vertebra Dissection).

How vertebrae are derived
-------------------------
- The label map is analyzed to estimate three canonical keypoints per vertebra (body, left pedicle, right pedicle).
- One :doc:`SpineData <../SpineData>` vertebra is created per detected keypoint triplet.
- If per-vertebra masks are provided, they are attached to the corresponding vertebra and converted to meshes automatically.

.. note::
    This conversion does not assign anatomical type names (C/T/L numbering).