First Point

Specifies the first point of the spline, either the first fit point or the first control
vertex, depending on the current method.

Next Point

Creates additional spline segments until you press Enter.

Undo

Removes the last specified point.

Close

Closes the spline by defining the last point to be coincident with the first. By default,
closed splines are periodic, maintaining curvature continuity (C2) along the entire
loop.

Method

Controls whether the spline is created with fit points or with control vertices. (SPLMETHOD
system variable)

Fit

Creates a degree 3 (cubic) B-spline by specifying fit points that the spline must
pass through. When the tolerance value is greater than 0, the spline must be within
the specified tolerance distance from each point.

Control Vertices (CV)

Creates a spline by specifying control vertices. Use this method to create splines
of degree 1 (linear), degree 2 (quadratic), degree 3 (cubic), and so on up to degree
10. Adjusting the shape of a spline by moving control vertices often provides better
results than moving fit points.

Object

Converts 2D or 3D quadratic or cubic spline-fit polylines to equivalent splines. The
original polyline is retained or discarded depending on the setting of the DELOBJ
system variable.

Knots

Specifies the knot parameterization, one of several computational methods that determines how the component curves between
successive fit points within a spline are blended. (SPLKNOTS system variable)

• Chord. ( Chord-Length method) Spaces the knots connecting each component curve to be proportional to the distances between each
  associated pair of fit points. An example is the green curve in the illustration.
• Square root. (Centripetal method) Spaces the knots connecting each component curve to be proportional
  to the square root of the distance between each associated pair of fit points. This
  method usually produces “gentlerâ€‌ curves.
• Uniform. (Equidistant method). Spaces the knots of each component curve to be equal, regardless
  of the spacing of the fit points. This method often produces curves that overshoot
  the fit points.

Start Tangency

Specifies a tangent condition on the starting point of the spline.

End Tangency

Specifies a tangent condition on the ending point of the spline.

Tolerance

Specifies the distance by which the spline is allowed to deviate from the specified
fit points. A tolerance value of 0 requires the resulting spline to pass directly
through the fit points. The tolerance value applies to all fit points except the starting
and ending fit points, which always have a tolerance of 0.