The MINC standard defines how spatial coordinates should be oriented relative to patients. Files are free to have data stored in the desired direction, but positive world coordinates are given a definite meaning in the medical imaging context. The standard is that the positive x axis points from the patient's left to right, the positive y axis points from posterior to anterior and the positive z axis points from inferior to superior.
The conversion of element index to world coordinates is done using the
dimension variable attributes
MIstart. If the direction cosines are
, then the vector between adjacent elements
along an axis is
. If and
MIdirection_cosines attributes for dimension (one of
then the first element of the image variable is at world coordinate
If the direction cosines are not present, then they are
assumed to be for
MIyspace and for
MIzspace. Direction cosines are
unit vectors and should be normalized. As well, the step attribute
should carry the information about axis flipping (negative or
positive) rather than the direction cosine.