Slicer3:Coordinates

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.