SPLINE

SPLINE draws a smooth, free-form curve. Use it for shapes that are not made of lines and arcs, such as a contour line or a curved edge.

How it works

Type SPL and press Enter. Musa CAD shows the current settings, then asks for points. Click the points the curve should pass through. Press Enter to finish.

Command line

Command: SPL
Current settings: Method=Fit   Knots=Chord
Specify first point or [Method/Knots/Object]: 0,0
Enter next point or [start Tangency/toLerance]: 20,25
Enter next point or [end Tangency/toLerance/Undo]: 40,5
Enter next point or [end Tangency/toLerance/Undo/Close]: 60,30
Enter next point or [end Tangency/toLerance/Undo/Close]: 80,10
Enter next point or [end Tangency/toLerance/Undo/Close]: Enter

The same five points used by the Fit and CV methods.

Plotted by Musa CAD 0.8.0 from the example drawing cmd-spline.musaDownload the drawing

Fit and CV

SPLINE has two methods. Switch between them with Method. Musa CAD keeps your choice for next time.

• Fit (the default): the curve passes through every point you give.
• CV: the points are control vertices. They make a frame that pulls the curve toward it. The curve touches only the first and the last point.

With CV, the prompts change. SPLINE starts with Current settings: Method=CV Degree=3 and Specify first point or [Method/Degree/Object]:, then asks Enter next point:, Enter next point or [Undo]: and Enter next point or [Close/Undo]:.

Options

Option	What it does
Method (M)	Enter spline creation method [Fit/CV] <Fit>:. Choose Fit or CV.
Knots (K)	Fit only. Enter knot parameterization [Chord/Square root/Uniform] <Chord>:. Sets how the curve is spread between your points. The three choices give slightly different shapes when the points are unevenly spaced.
Degree (D)	CV only. Enter degree of spline <3>:, a whole number from 1 to 10. Degree 1 joins the points with straight lines; the default, 3, gives a smooth curve.
Object (O)	Asks Select spline-fit polylines:. Each polyline you select becomes a spline. A polyline smoothed with the Spline option of PEDIT keeps exactly the same curve. Any other polyline becomes a spline through its vertices.
start Tangency (T)	Fit, before the second point. Specify start tangent:. Click a point, and the curve leaves the first point heading toward it. Press Enter to leave the start free.
end Tangency (T)	Fit, from the second point on. Specify end tangent:. Click a point, and the curve ends heading toward it. This also finishes the spline.
toLerance (L)	Fit only. Specify fit tolerance <0.0000>:. With 0 the curve passes through every point. A larger value lets it pass within that distance of the points, which can make it smoother.
Undo (U)	Removes the last point.
Close (C)	Joins the curve back to the first point and finishes. With Fit, the curve runs smoothly through the join. You need at least three points.
Enter	Finishes the spline.

Good to know

• Esc throws away the spline you are drawing. Press Enter to keep it.
• A spline needs at least two points. Pressing Enter after one says A spline needs at least two points. and nothing is drawn.
• Close with fewer than three points says Close needs at least three points.
• The method, knots and degree are kept until you close Musa CAD. The tolerance starts at 0 every time.
• A tolerance has no effect on a closed spline, or on one with a start or end tangent.
• With fewer points than the degree plus one, the degree is lowered to fit. Two points give a straight line.
• A tangent point on top of the end point is refused with The tangent needs a point away from the spline's end.
• A Fit spline keeps its fit points. Its grips sit on them, and dragging one fits the curve again.

Compared with AutoCAD

SPLINE uses AutoCAD’s prompts for its Fit and CV methods, with the same options: Knots, Degree, Object, start and end Tangency, toLerance, Undo and Close.

Next

• Change a spline’s points and shape with SPLINEDIT.
• Join the ends of two objects with a smooth curve using BLEND.
• Smooth a polyline into a curve with PEDIT.