Creating Straight Line Segments

Straight-line segments can be created and maintained within a curve between two adjacent data points. This is done through the specification of particular data point types.

A curve will be straight between two data points if each of the data points satisfy one of the following conditions:

• Both data points are tangents (type Tangent) and their tangency controls are collinear.

• Both data points are knuckles, and one or both either have no tangency controls on the side of the straight segment, or the tangency controls are collinear with the straight line through the two data points.

• If one data point is an end point of type Ordinary, and the other point corresponds to one of the above criteria, or is of type Tangent(auto).

For illustrations of how to create straight segments within curves, see Figures 3:63 and 3:64 below.

Figure 3:63. Straight segments at the beginnings and ends of curves

Figure 3:64. Straight segments within curves

A common requirement is to straighten a region of a curve whilst maintaining smooth tangency conditions at both ends. This can be done quickly using the following procedure:

Straighten a region of a curve

1. Select a data point marking one end of the segment to be straightened. Hold <Ctrl> and select the point marking the other end.

2. Click (or select GEOMETRY \ STRAIGHTEN) to straighten the segment

The segment is straightened by removing all data points between the selected segment ends, then setting the types and tangency controls of these bounding points appropriately

Note: The purpose of Tangent(auto) data points is to create straight segments when they are adjacent to either a curve end point (type Ordinary), or a knuckle that has no tangency control on the same side. If neither of these conditions apply, Tangent(auto) data points are have the same effect on the shape of the curve as Ordinary points.

For additional information see Curve, Data Bar - Data Points Grid and Curves Graphical Reference.