| xform {RNifti} | R Documentation |
These functions convert the “qform” or “sform” information in a NIfTI header to or from a corresponding affine matrix. These two “xform” mechanisms are defined by the NIfTI standard, and may both be in use in a particular image header. They define the relationship between the storage order of the image and real space.
xform(image, useQuaternionFirst = TRUE) qform(x) <- value sform(x) <- value orientation(x, useQuaternionFirst = TRUE) orientation(x) <- value
image, x |
An image, in any acceptable form (see
|
useQuaternionFirst |
A single logical value. If |
value |
A new 4x4 qform or sform matrix, or orientation string. If a
matrix has a |
For xform, an affine matrix corresponding to the “qform”
or “sform” information in the image header. For orientation, a
string with three characters indicating the (approximate) orientation of
the image. Each character may be ‘R’ for left-to-right, ‘L’ for
right-to-left, ‘A’ for posterior-to-anterior, ‘P’ for
anterior-to-posterior, ‘S’ for inferior-to-superior, or ‘I’ for
superior-to-inferior. The replacement forms return the modified object.
The qform and sform replacement functions are for advanced users only. Modifying the transforms without knowing what you're doing is usually unwise, as you can make the image object inconsistent.
Jon Clayden <code@clayden.org>
The NIfTI-1 standard (http://www.nitrc.org/docman/view.php/26/64/nifti1.h) is the definitive reference on “xform” conventions.
im <- readNifti(system.file("extdata", "example.nii.gz", package="RNifti"))
xform(im)
# Remove the qform information
qform(im) <- structure(diag(4), code=0L)
# The same as above, since the sform is unmodified
xform(im)