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Dimension Attributes

Each dimension has a class that specifies its overall interpretation: spatial, temporal, spatial frequency, temporal frequency or user-defined (i.e. arbitrary) dimension. The following shows the list of dimension classes which are defined in minc 2.
  1. MI_DIMCLASS_ANY - Don't care (or unknown)
  4. MI_DIMCLASS_SFREQUENCY - Spatial frequency
  5. MI_DIMCLASS_TFREQUENCY - Temporal frequency
  6. MI_DIMCLASS_USER - Arbitrary user-defined axis
  7. MI_DIMCLASS_RECORD - Record as dimension

The above definition also creates a more flexible naming convention where any name can be defined as any dimension class.

Apart from name and class, MINC 2 has a number of other attributes defined for each dimension which specify how the data should be interpreted.

The description attribute is used to specify human-readable text which provides some information about the interpretation of the dimension. For example, it is commnly used to describe the dimension's orientation relative to the patient. The description attribute is set to default text only for the named dimensions xspace, yspace, zspace but can be set for any dimension by the user. For instance, xspace is defined to increase from patient's left to right.

The unit attribute, also a human-readable text, that defines unit of the distance between the sampled data points along each dimension. The default unit attribute is set to millimeters (i.e., ``mm'').

The spacing dimension attribute is a human-readable text which defines whether the sampled data points are in constant or random intervals from each other (i.e., regular versus irregualr) in space from each other. The spacing attribute is set to ``regular__'' by default.

The start attribute is a number which specifies the position of the first sampled data point in world coordinates (refer to voxel versus world subsection). This attribute is set to zero by default. The step attribute is a positive number indicating the size of the interval between sampled data points along a regularly sampled dimension. A negative value simply indicates that the sampled data points have a reverse orientation. This attribute is set to one by default. An irregularly sampled dimension must define a list of interval values defined for each pair of sampled data points which is defined in MINC 2 as offset property.

The length attribute is a number defining the total number of sampled data points along a dimension. The direction_cosines attribute are a set of three vectors associated with spatial dimensions and define the precise orientation of the axis relative to "true" x, y, or z coordinates. ** NOT sure whether to list all the attributes or not **

next up previous contents
Next: Voxel and World Coordinate Up: Dimensions and coordinate systems Previous: Dimensions MINC 2.0   Contents
Robert VINCENT 2004-05-28