iFit/imroi

 imroi: define a region of interest on a data set
 
 b = imroi(a)
  This function allows to select regions-of-interest (ROI) over an existing 
    data set, which defines areas where data points are selected. The selected 
    data set is returned, with NaN's elsewhere.

 The mouse is used to define points/lines in the data set. Click on the plot to 
   define the limits of the selection. These vertices are used as a polygon
   shape which intersection with the data set defines the selection.

 You may undo (remove) previous points/lines from the active polygon by pressing
   the mouse right-button or the BackSpace key. To clear the current ROI and start
   over, press the 'c' or DEL key.

 It is possible to define as many separate ROI's by pressing the 'a' key to add
   to store the current polygon, and start a new one.

 When used with surfaces and volumes, you may rotate the view (using the Rotate 
   icon from the toolbar or Tools menu) by pressing the 'r' key over the figure.
   This stores the current polygon definition, and switch to the rotate mode.
   Once the view is properly oriented, disable the Rotate tool (click again on 
   the rotate icon) to enter a new polygon definition.
   You may alternatively use the up/down/left/right arrows to rotate the view.

 Once all ROI's are defined, press the middle mouse button or the Return key to
   end the ROI selection and compute the intersection with the data set.

 To abort (cancel) and exit the ROI tool, use the Escape key.

 [b, mask] = imroi(a)
  Same as above, but returns the mask data set, which contains 0 and 1.
  and we have b=a(mask);

 [b, mask, f] = imroi(a)
  Same as above, but returns the selection figure handle.

 [b, mask] = imroi(a, options)
  The options are used to customize the plot rendering, see iData/plot.

 Interaction:
     mouse left-click or SPACE  add a point/line
     right-click or BACKSPACE   remove last point
     DEL or "C"                 remove all points
     return or "Q" or middle-click: terminate input and compute intersections
     A                          start a new separate polygon (add)
     R                          change orientation (2D/3D). Disable rotation to continue ROI.
     ESC                        abort
     H                          display a help dialogue
     left/right/up/down arrows  rotate the view

 Example:
  a = iData(peaks); b=imroi(a);

  input:
     a: a data set (iData)

  output:
     b:    the data set with selected area (iData)
     mask: the mask used for the selection, with 0 and 1 as Signal (iData)
     f:    figure used to define the selection

 Version: Nov. 27, 2018
 See also iData, iData/plot, iData/edit