SYNOPSIS:
    volume: a combination of three fields that describe a normal
            dataset for rendering.

DESCRIPTION:
    Most eccet renderers expect at least a grey/norm field to be
    present in the dataset. To add segmentation information to the
    field a classfield needs to be allocated. To speed up rendering,
    many renderers require a depth field.

    However, there is more to a volume than just the datafields.
    Volumes also carry associated metadata that can e.g. be used
    to determine the physical sizes of the volume, determine the
    meaning of grey values (e.g. HU mapping) or carry other information
    related to the dataset (like the patient's name).

SEE ALSO:
    field, norm, grey, class, depth, VOL_ADD
