Landmarks

This page enables you to place landmarks on images associated with a prerecorded data set. You can then make measurements of distances and angles between these landmarks. You can also include fiducial landmarks located using a tracked pointer in these measurements.

The landmarks task can be selected either by using the tabs at the top of the task pages, or by selecting from the task menu, or by selecting the landmarks tool in the toolbar.

Landmarks can be created by using a pointer attached to a position sensor to locate points in 3D space as described on the pointer task page, and pressing the 'Grab pointer location' button. Alternatively, you can just click on locations in the review (top left) or reslice windows after selecting the landmark tool.

When defining landmarks in any of the reslice visualisations (but not in the review window), the default behaviour is to move the landmark slightly so that it is located at the nearest point in 3D on the nearest frame. This frame is then automatically shown in the review window. In a normal data set this movement will not be perceptible, unless you define a landmark outside of the recorded data. This behaviour can be disabled by un-checking the 'Snap mouse clicks to frames' checkbox. Note that if disabled, landmarks can be defined anywhere in space, and hence may not show up on any of the recorded frames, though they will always be displayed in the 3D window.

All the landmarks you have defined are listed, in alphabetical order, in the box at the top of the landmarks task page. Up to three landmarks can be selected from this list using the left mouse button. If you select more than three, the least recently selected landmark will be deselected to make way for the new one.

As you select a landmark, its name is highlighted and it will be allocated to one of the slots A, B or C. You can then change the landmark's name by editing the text in the appropriate slot and pressing return. A selected landmark can be deselected by clicking on its name again. The distances and angles between the selected landmarks are displayed at the bottom of the window.

Next to each of the selected landmarks A, B and C, there is a 'Delete' button. Note that this deletes the landmark completely. If you just wish to deselect the landmark, you should click on the landmark name in the box at the top of the task page.

Finally, each selected landmark also has a 'Find' button. This button can be used to locate orthogonal views which intersect with the landmark, as well as the nearest frame.