Function head_box 

fn head_box(
    data: &[f32],
    dims: [usize; 3],
    margin: usize,
) -> Option<[(usize, usize); 3]>

The head’s bounding box in the normalised, padded C-order volume data: the largest face-connected region above HEAD_THRESHOLD, grown by margin voxels on every side and rounded out to multiples of LATTICE (dims are multiples of it already). None when nothing is above the threshold or the box is the whole volume.