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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:
- Native file order - The dimension's direction is exactly as it
appears in the file.
- Counter file order - The dimension's direction is opposite the
file order.
- 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.
- 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.
Next: Volume Attributes
Up: Dimensions and coordinate systems
Previous: Coding Examples
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Robert VINCENT
2004-05-28