MINC dimensions may have either regular or irregular spacing. Regularly-sampled dimensions are sampled at a constant interval, while irregularly-sampled dimensions are sampled at arbitrary positions along the axis.
Because regular dimensions are sampled at a constant interval, they are fully defined by their origin and step size. Therefore, the dimension variable for a regular dimension contains no meaningful data.
For an irregular dimension, the value of the dimension variable must be a vector with a length equal to the number of sampled points along the dimension. The value of the vector at a given index gives the value of the dimension at that sample point.