Hi Matt,

An AFNI dataset consists of a collection of 3D volumes
(possibly over time, possibly multiple statistics, etc).
Each 3D volume is nx voxels by ny voxels by nz voxels
(the number of voxels in each of x, y and z directions).

For a single voxel (out of nx*ny*nz), the i, j and k
values are the indices for that voxel in the x, y and z
directions. So i is in {0..nx-1}, j is in {0..ny-1},
etc.

The origin of a dataset is the xyz coordinate of the
voxel with indices (0,0,0), i.e. the first voxel in the
dataset.

So the xyz coordinate of voxel (i,j,k) is:

(Ox + i*dx, Oy + j*dy, Oz + k*dz)

where (Ox,Oy,Oz) are the xyz-coordinates of the origin.

Running '3dinfo' on a dataset will provide information
about the origin, orientation, etc.

----

For more information, consider the class handouts on this
web site. Under the top-level location:

[afni.nimh.nih.gov]

You might view "Introduction and Overview of AFNI":

[afni.nimh.nih.gov]

or perhaps "Image Input to AFNI - to3d and other data formats":

[afni.nimh.nih.gov]

- rick