Dimension and voxel ordering

Since MINC files may organize data arbitrarily, the MINC 2.0 programming interface allows the programmer to specify both the apparent order of dimensions and the apparent direction of each dimension. This enables programs to specify a that the data be presented in whatever fashion is most convenient.

The programmer may set an ``apparent'' dimension order for a given volume. Specifying an apparent dimension order causes the library to transform all coordinates and data as if the data was stored in the apparent order. If a set of three volumes which must be processed simultaneously have the dimensions x,y,z, z,y,x, and y,z,x respectively, it may be useful for a program to treat them each as if the data was in z,y,x order.

Transforming the dimensions of a block of data causes the block to be restructured in memory after it is read or before it is written. Obviously this restructuring takes time and will affect data throughput.

If the apparent dimension order happens to match the volume's file dimension order, no special processing is performed.

For each dimension, a programmer may also specify an apparent direction. This apparent direction may be specified in one of four ways:

1. Native file order - The dimension's direction is exactly as it appears in the file.
2. Counter file order - The dimension's direction is opposite the file order.
3. Positive order - The dimension's direction in world coordinates is guaranteed to be positive along increasing voxel coordinates. This mode inverts the dimension only if the step size is negative.
4. Negative order - The dimension's direction in world coordinates is guaranteed to be negative along increasing voxel coordinates. This mode inverts the dimension only if the step size is positive.