Slicer3:Coordinates
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Coordinate Definitions
This page describes the coordinate system assumptions for Slicer3
Volumes
IJK refers to voxel index coordinates.
RAS refers to Right-Anterior-Superior subject-referenced coordinates.
Each volume includes a transformation to go from voxel indices (IJK) to world (RAS). This is obtained with the vtkMRMLVolumeNode::GetRASToIJKMatrix(vtkMatrix4x4).
Models
Model vertices are expressed in millimeters, in RAS space.
Fiducials
Fiducial points are expressed in millimeters, in RAS space.
Transforms
All transforms at RAS to RAS transforms.
Notes
- image data in a volume is laid out in memory in the same order as it is read from disk. That is, the "infamous VTK Y-flip" is not applied.
- the reader for each file type is required to provide the IJKToRAS mapping.