Using Split Points

When creating a patch boundary network, it is often desirable to use only certain parts of curves. For example, the waterlines needed to form patch boundaries in the afterbody may differ from those needed for patch boundaries in the forebody. Prior to the introduction of split points in PACE M3, the user had to permanently delete regions of curves that were not to form patch boundaries. Now, active curves can be split into arbitrary regions, which can be independently specified as Active and Inactive. When a surface is built, patch boundaries will only be formed by active regions. Active regions are displayed with a solid line, and inactive regions with a feint dotted line, as shown in Figure 3:104 below.

Figure 3:104. Split points displayed on active curves. Only the solid regions of these curves will be used to form patch boundaries.

A curve is divided into regions by split points. In order to change the active regions of a curve, the split points must be displayed for the curve.

Display split points

1. Select the Right Mouse button on an active curve in a graphics view, and then select DISPLAY SPLIT POINTS from the popup menu.

   Alternatively, check the box in the Split Points column of the Curves grid in the Data Bar.

2. Select the Right Mouse button in this column to launch a popup menu that gives control of split points display for selected groups or all active curves.

3. Turn off the split points display by unchecking these boxes, or by clicking the Right Mouse button on a region of the curve and selecting QUIT DISPLAY from the popup menu.

Whilst a curve's split points are displayed it cannot be modified by moving data points or control points, so the display of these is disabled. All split point editing operations require that split points be displayed. Split points are displayed with a small diamond-shaped symbol, shown in Figure 3:104 above. When they are displayed, the user can toggle the active status of the separate regions of the curve that lie between them, by clicking the Right Mouse button on the region and selecting ACTIVE.

Split points are added to one curve at a time. First split point insertion mode must be started (this works in a similar way to data point insertion mode - see Adding data points).

Start split point insertion mode

4. Either click the Right Mouse button on any of part of the curve and selecting SPLIT from the popup menu, or select the curve by clicking the Left Mouse button on it in a graphics window.

5. Select CURVE \ INSERT SPLIT POINTS or .

   The cursor changes to a symbol. Each click of the Left Mouse button in a graphics window causes a split point to be inserted into the curve at the point nearest to the cursor.

6. Double-click the Left Mouse button to inserts the final split point, and exit split point insertion mode.

   Alternatively, exit split point insertion mode by selecting CURVE \ INSERT SPLIT POINTS again, or clicking <Esc>.

7. Split points are deleted by selecting them using the Left Mouse button and clicking <Del>.

This works for groups of split points selected whilst holding <Ctrl>, or using a rubberband box. Other deleting options are available from the popup menu launched by clicking the Right Mouse button on a split point:

• DELETE - Deletes the single split point.

• DELETE ALL - Deletes all the split points within the same curve.

• CLEAN - Deletes all split points in the same curve that lie between two regions that have the same active or inactive status (such split points are redundant).

Like other point entities, split points can be dragged with the cursor whilst holding the Left Mouse button on them in graphics windows. This has the effect of sliding them along the curve like beads on a wire. A split point cannot be dragged beyond its neighboring split points. Also, split points can only be moved one at a time, and cannot be nudged with the arrows keys.

When positioning split points, it is best to allow a little overlap between active regions that are supposed to intersect each other.

Inactive regions of a curve can be used to overcome a common form of topological ambiguity that prevents a surface from being built correctly - see Boundary network is topologically ambiguous.