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= Control Points =

Control points are used in surface construction. Every subject has an associated {{{control.dat}}} file in their {{{tmp}}} directory; this is the list of control points, in Talairach space, that is read in to TkMedit automatically upon start.

== Display Options ==

Control points appear as green cross hairs in the Display Window. They can be turned off by unchecking '''Views->Control Points'''.

== Editing ==

Control points can be edited with the Edit Control Points tool, which can be activated by pushing the {{attachment:Icons/TkMedit/icon_edit_ctrlpts.gif}} button on the Main Toolbar, by choosing '''Tools->Edit Control Points''', or by pressing the 'c' key when the mouse is in the Display Window.

To make a new control point, click anywhere in the Display Window with mouse button 2. To remove a control point, click near it with mouse button 3. Button 3 will remove the closest control point to the voxel clicked, within 3 voxels.

== Saving ==

Whenever a new control point is made, it is automatically written to the {{{control.dat}}} file. However, removed control points are not removed from the file until you choose '''File->Save Control Points''' or quit normally with the '''File->Quit''' command.

In normal cases, the {{{control.dat}}} file is saved in the subject's {{{tmp}}} directory, so the FreeSurfer programs that use the file know where to find it. However, if you used the {{{-f}}} option to load a volume file by name, not specifying a subject name and directory, you will see a warning when you try to write a control point, and the file will be saved in the current working directory.  This file can then be moved to a subject's {{{tmp}}} directory later.