| Re: arbitrary rotation of 3-d arrays [message #15728] |
Thu, 10 June 1999 00:00 |
David Foster
Messages: 341
Registered: January 1996
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Senior Member |
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D. Mattes wrote:
>
> hello idl users:
> has anybody out there in idl-land written or seen code to apply arbitrary
> rotations to 3-d arrays???
>
> thanks in advance!
>
> david mattes
Are you talking about rotating the entire array, as opposed to
extracting a 2D slice out of the array? If so, you might want to
look into AIR (Automated Image Registration), a package written
at UCLA:
http://bishopw.loni.ucla.edu/AIR3/ (AIR Automated Image Registration)
The C source is available, so if you need to integrate it with IDL
you could modify it appropriately. This program was intended for
use with medical images, don't know how general it is, but it works
well, at least for our brain images.
If you don't find what you want, email me offline and I can probably
help come up with something. I don't think it would be too difficult.
Basically once you've chosen an origin about which to rotate the array,
you would generate a 4D fltarr for the volume whose values correspond
to the three indices, then compute the affine transformation matrix
for (1) translation to the origin; (2) rotations; (3) scale factors
if you want; and (4) translate back to the original origin, all using
T3D. Then transform the coordinates using:
vol_ind(*,*,*j) = vol_ind(*,*,*) # !P.T(*,*,*)
(!P.T is computed by T3D).
Similar code for the 2D case of extracting a slice from a 3D volume
can be seen in $IDL_DIR/lib/extract_slice.pro, but be aware that:
1) You will get incorrect results if any of the rotations
results in an exchange-of-axis (near 90 degrees); these
must be applied first.
2) This routine does not account for anisotropic voxels.
Dave Foster
--
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~
David S. Foster Univ. of California, San Diego
Programmer/Analyst Brain Image Analysis Laboratory
foster@bial1.ucsd.edu Department of Psychiatry
(619) 622-5892 8950 Via La Jolla Drive, Suite 2240
La Jolla, CA 92037
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