Angle Span

The figure below illustrates how the curvature of a segment is affected by the angle span parameter q.

Effect of angle span on the curvature of the segment joining two vertices.

As shown in the figure above, the smaller the angle span, the smaller the curvature of the circular arc that joins the two vertices. When the angle span is 0°, the arc degenerates to a straight segment.

Segments in a wireframe are also identified by indices: the segment joining the vertex N to N+1 is indexed by N. For example, the index of the segment between the vertex 0 and 1 is 0.

The angle span parameters in the figure above are both positive. The angle span of a segment N is defined positive if the arc that joins the vertex N to N+1 is in the direction of positive rotations. The sign of the span angle determines the concavity of the segment. In the figure above the coordinate frame is left-handed and the direction of positive rotations is clockwise. If you specify a negative angle span in that coordinate frame, the arc segments reverse their concavity as shown in the figure below.

The effect of negative angle span on the concavity of the segment