This part of the Standard makes use of the following terms defined in PS 3.15:
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3.17 Multi-Dimensional Definitions
3.17.1 Reference Coordinate System (RCS) : The RCS is the spatial coordinate system in a DICOM Frame of Reference. It is the chosen origin, orientation and spatial scale of an Image IE in a Cartesian space. The RCS is a right-handed Cartesian coordinate system i.e. the vector cross product of a unit vector along the positive x-axis and a unit vector along the positive y-axis is equal to a unit vector along the positive z-axis. The unit length is one millimeter. Typically, the Image IE contains a spatial mapping that specifies the relationship of the image samples to the Cartesian spatial domains of the RCS.
3.17.2 Fiducial: A fiducial is some unique feature or landmark suitable as a spatial reference or correlation between similar objects. The fiducial may contribute to the definition of the origin and orientation of a chosen coordinate system. Identifying fiducials in different data sets is a common means to establish the spatial relationship between similar objects.
3.17.3 Fiducial Point: A Fiducial Point defines a specific location of a Fiducial. A Fiducial Point is relative an image or to an RCS.