-------------------------------------------
entry variable: $xtalairach -- Right/Left
entry variable: $ytalairach -- Posterior/Anterior
entry variable: $ztalairach -- Inferior/Superior
-------------------------------------------

The coordinates in the three entries in the left
middle column:

  "yTal P/A:"
  "xTal R/L:" 
  "zTal I/S:"

are updated upon a left-click on the displayed
image.  Entering a number plus <Return> will move
the cursor to that coordinate (keeping current
display plane).  Left-click the middle "xTal R/L"
label to go to the pixel nearest Talairach x=0,
y=0, z=0.  Left-click the bottom "zTal I/S" label
to report Talaiarch coordinates in x,y,z order
(N.B.: Talairach x is in middle).

For brains reconstructed with (old/ancient)
SubjectTools in FreeSurfer0.8, the linear
transformation matrix for these Talairach
coordinates is generated using the Montreal
Neurological Institute Automated Linear
Registration Package described in:

  DL Collins, P Neelin, TM Peters, AC Evans (1994)
  J. Comp. Assist. Tomogr. 18:192-.

The software was downloaded from:

  ftp://ftp.bic.mni.mcgill.ca/pub/mni_autoreg/

For brains reconstructed with MGH freesurfer, the
Talairach coords can be generated using several
different procedures depending on the arguments
to recon-all.

The internal coords -> Talairach coords
transformation matrix is read by default from
<subject>/mri/transforms/talairach.xfm.  The
inverse matrix (for converting Talairach ->
internal coords) is automatically calculated
upon reading it (see below).

For .mgz/.mgh files, the volume center is read
from the last line of the direction cosine
transformation matrix in the header (c_r, c_a,
c_s) and is added to the currently selected
intrinsic coordinate before applying the
Talairach transformation matrix.  Conversely, the
inverse Talairach transformation matrix is first
applied to a Talairach point and then the
intrinsic center subtracted afterward.

The unlabeled entries below each Talairach
coordinate (immediately to the right of the
sliders) are the integer internal coordinate
pixel indices.  These are formatted slightly
differently in MGH tkmedit.  The equivalent
("Volume index") for MGH tkmedit is always
written into the tkmedit title bar.

Tcl commands

To read an MNI-style Talairach transform from a
different file, use:

  set transform /some/other/talairach.xfm
  read_invert_mni_tal

To interactively read an arbitrary 3x4 (rows by
cols) Talairach transformation matrix, use:

  read_invert_12_tal <r1c1> <r1c2> ... <r3c4>

which has 12 arguments (3 concatenated rows).
Accepts scientific notation (e.g., -1.80802e-02)
