### The Curve Editor

The middle mouse button can be used to edit segmentation curves in the `Review' window and manifold definitions in the `Reslice' window. The user traces out an
**edit curve** with the middle mouse button. The edit curve
replaces a portion of the **old curve** as follows.

In the `Reslice' window, for defining the manifold shape, if the
edit curve intersects the old curve more than once, then the old curve
is replaced with the edit curve between the first and last points of
intersection. Bits of edit curve outside the intersections are
irrelevant. If the edit curve intersects the old curve only once, then
the longer bit of the edit curve is spliced on to whichever bit of the
old curve it joins most smoothly, replacing the other bit of the old
curve.

In the `Review' window, for editing segmentation contours, the
edit curve must intersect the old curve at least twice. Only the first
and last intersections count. One of the sub-curves of the old curve
between the intersections will be replaced by the edit curve. Which
sub-curve is replaced is determined as follows. If both joins between
the curves can be made smooth by replacing one particular sub-curve,
then this will be the sub-curve that gets replaced. If the
intersection angles conflict, so that one has to be acute, then the
shorter sub-curve will be replaced.

If Stradx replaces the wrong portion of curve in either the
`Reslice' or `Review' windows, simply click once with the middle mouse
button to toggle the replaced section.