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.
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An image, in any acceptable form (see
A single logical value. If
A new 4x4 qform or sform matrix, or orientation string. If a
matrix has a
xform, an affine matrix corresponding to the “qform”
or “sform” information in the image header. For
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 <[email protected]>
The NIfTI-1 standard (http://www.nitrc.org/docman/view.php/26/64/nifti1.h) is the definitive reference on “xform” conventions.
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