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# adding orientation to itkimage - PowerPoint PPT Presentation

Adding Orientation to itkImage. Motivation. Image Coordinate Systems. Coordinate systems are an important part of any medical application. Medical scanners create regular, &quot;rectangular&quot; arrays of points and cells. The topology of the arrays is implicit in the representation.

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Presentation Transcript

Image Coordinate Systems
• Coordinate systems are an important part of any medical application.
• Medical scanners create regular, "rectangular" arrays of points and cells.
• The topology of the arrays is implicit in the representation.
• The geometric location of each point is also implicit.
vtk and itk images
• vtk and itk store meta-information that can be used to convert between image coordinates (i-j-k) and world coordinates (x-y-z).
• Each image has an origin that is a 3-D (n-D for itk) vector. The origin (x-y-z) specifies the world coordinate of the first point in memory. The spacing specifies the distance between points along each axis.
• Using the spacing and origin, the transformation between i-j-k and x-y-z is a fast, simple computation.
• x(yz) = origin + i(jk) * spacing;
• i(jk) = (x(yz) - origin) / spacing;

(image)

slow

fast

medium

Requirement: Location + Orientation

space: right-anterior-superior

space origin: (117.5,-93,119)

space directions: (-0.859375,0,0)(0,0,-0.859375)(0,5,0) none

(RAS)

superior

anterior

right

Proposed extensions to itk::Image
• Add an itk::Matrix containing direction cosines
• The i-j-k -> x-y-z transformation could include the orientation in the computation.
• Adding the matrix will not change the existing API.
• Almost all index to point calculations are confined to itk::Image.
• The transformations in matrix form are:
• XYZ = To* Rc * Ss * IJKwhere To is a translate to the origin, Rc is the matrix of direction cosines and Ss is a scale matrix of spacings.
• There are performance considerations, so the implementation may cache some internal matrices and state.
Next Steps
• Continue discussion on the Wiki
• NAMIC Wiki:Community Coordinate Systems