2004

Modify Objects | 419
You can delete fit points of a spline, add fit points for greater accuracy, or
move fit points to alter the shape of a spline. You can open or close a spline
and edit the spline start and end tangents. Spline direction is reversible. You
can change the tolerance of the spline also. Tolerance refers to how closely the
spline fits the set of fit points you specify. The lower the tolerance, the more
closely the spline fits the points.
Refine the Shape of a Spline
You can refine a spline by increasing the number of control points in one
portion of the spline or by changing the weight of specific control points.
Increasing the weight of a control point pulls the spline more towards that
point. You can also refine a spline by changing its order. A spline’s order is
the degree of the spline polynomial + 1. A cubic spline, for example, has
order 4. The higher a spline’s order, the more control points it has.
Consider the following example. You have created a spline to represent a
geographic contour. Grips are turned on, and you need to move the fourth
fit point to increase accuracy. When you select the spline, grips appear at the
control points. If you created the spline by fitting it through a set of points,
and you haven’t purged this information using the Purge option of the
SPLINEDIT command, and you select the Fit Data option, grips appear at the
fit points on the selected spline instead of at the control points.
spline with fit
tolerance=0
spline with fit
tolerance=.5
control
points
control
points
fit pointsfit points