Point Correspondences

Defines pairs of 3D landmarks for image registration and error evaluation.

Input

Two 3D volumes.

Output

The transformation of one of the input volumes is changed when the registration is applied. The actual landmarks may be exported to, and imported from, the annotation model as well as text files.

Description

The module provides a GUI for successively defining a set of anatomical landmarks on two 3D volumes. It automatically blends the views to highlight the volume which is currently selected for point placement. At every point, the current mean error is displayed between the two sets of points, and automatically updated if the transformation of either of the images is changed, e.g. by image-based registration algorithms. The module therefore interacts with the Image Registration module, and can be used as its error function if both are open at the same time.

Coordinates: Either set of points is chosen to either be in image or in world coordinates, in the first case they move with the transformation of the image. This setting affects which image is moved when the Registration button is clicked (the one whose points are in image coordinates). If both point sets are in world coordinates, the registration moves the second input image as default. The chosen coordinate system also affects loading and saving the point correspondences to and from text files via the Load and Save buttons. The additional checkbox voxel only affects load and save, it denotes whether voxel coordinates instead of mm values are to be used.

Registration: For one or two point correspondences, only a translation is computed. For three or more correspondences, a least-squares fit of the best rigid transformation between the point sets is computed and applied. If Auto correspondences is enabled, the matching is also established automatically.