Editing Non-Fitted Curves

The only way of manipulating a curve that has no data points is via its control points. Correspondingly, using control points to manipulate a curve breaks any positional correspondence of that exists between the curve and its data points. This represents a lower level of interaction - manipulating data points alters the vertices indirectly to effect changes in the curve. A brief summary of the differences in the approaches is as follows:

Table 3: 2. The differences between the use of data points and control points.

The fact that Lines is oriented more toward the use of fitted curves is reflected in the level of support for direct control points manipulation. For example, control points cannot be directly added or removed, and there are no equivalents to the Straighten function or the high-level tangent controls available when using data points.

The principals of selecting, dragging and nudging vertices are identical to those concerning data points. There are fewer operations associated with control points; in fact their position is the only attribute that can be changed. Their number can be altered indirectly, by fitting the curve and adding and removing data points.

The graphical display of control points is turned on and off in the Curves grid on the Data Bar. Control point positions can be edited numerically in the Control Points grid of the Data Bar, including copy <Ctrl+C> and paste <Ctrl+V> operations. As with data points, a control point will highlight when the cursor is over it. It can then be selected and moved by holding down the Left Mouse button and moving the mouse:

Figure 3:69. Dragging a single control point.

The co-ordinates of the control point being dragged will be highlighted and updated if the Control Points grid is visible.

Holding <Shift> whilst dragging control points constrains the movement to either the horizontal or vertical direction. Control points dragged in the oblique view move in the pre-specified stylus direction in the same way as data points.

Selections of multiple control points can be achieved in an identical way to selecting multiple points, except that <Shift> cannot be used to make contiguous selections. First select an initial control point, hold <Ctrl> and then:

• Select additional control points by clicking the Left Mouse button.

• Drag a rubber-band selection box whilst keeping the Left Mouse button depressed.

Figure 3:70. Using a rubberband box to select multiple control points

Truncating Non-Fitted Curves

Truncating (trimming away part of the curve from one end) fitted curves is simply done by selecting the group of data points at the end in question and clicking <Del>. The same effect can be achieved for non-fitted curves, provided they do have a set of data points that are reasonably close to the curve. Deleting a number of data points from one end of a curve truncates the curve by clipping it to the point that is nearest to the selected data point that is sequentially furthest from the end.

Figure 3:71. Truncating a non-fitted curve by deleting data points

For additional information see Data Bar - Control Points Grid.