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Splines

May 20, 2011

Spline is a smooth curve that pass through a series of control points. You can control the fit tolerance among the curve and points,and apply the fitness to drawing irregular curves. A NURBS curve produces a smooth curve between control points.

A NURBS curve produces a smooth curve between control points.

Multiple points are required for drawing irregular splines And you can close the spline so that the start and endpoints are coincident and tangent.

Tolerance in command line prompts describes how precisely the spline fits the set of fit points you specify. The lower the tolerance, the more closely the spline fits the points.If the value is set to 0, the spline curve passes through the fit point.

If you set the tolerance value greater than 0, the spline will go through fit point within the specified tolerance range.

Usually two ways of creating splines are provided:

•      Create a spline converted from a polyline using Spline option of PEDIT command.

•      Create a spline using SPLINE command, that is NURBS curves

To draw a spline

1. Choose Draw > Spline.

2. Specify the first point of the spline.

3. Specify the second point of the spline.

4. Specify as many more points as you want.

5. When you have finished, press Enter.

Draw toolbar

Command line SPLINE

You can add tangents to the spline, which are lines that give it shape.

To add tangents to a spline

1. Specify the starting tangent point.

2. Specify the ending tangent point.

 Spline Spline with starting tangent point (A) and ending tangent point (B)

Specifying fit tolerance

By default, a spline passes through all of the control points. When you draw a spline, you can change this by specifying the fit tolerance. The fit tolerance value determines how closely the spline fits the set of points you specify. For example, a spline fit tolerance value of 0 causes the spline to pass through the control points. A value of 0.01 creates a spline that passes through the start and endpoints and within 0.01 units of the intermediate control points.

To specify the fit tolerance

1. Choose Draw > Spline.

2. Specify the first point of the spline.

3. Specify the second point of the spline.

4. To accept the default of 0.0000, press Enter. To specify a different fit tolerance, enter F and type the number, and then press Enter.

5. Specify the additional points you need to draw a spline or a closed spline.

Draw toolbar

Command line SPLINE

Drawing a closed spline

You can draw a closed spline, which is a spline for which the start point and endpoint are the same. Because the spline is closed, you specify only one tangent.

To draw a closed spline

1. Choose Draw > Spline.

2. Specify the first point of the spline.

3. Specify the second point of the spline.

4. Specify as many more points as you want.

5. When you have finished, on the command line, type close.

6. To complete the command, specify the tangent point.

Draw toolbar

Command line SPLINE

The start point and endpoint (A) of a closed spline.

Commands Reference

PEDIT: Edits polylines and three-dimensional polygon meshes

PLINE: Creates two-dimensional polylines

SPLINE: Creates a nonuniform rational B-spline (NURBS) curve

SPLINEDIT: Edits a spline or spline-fit polyline

System Variables Reference

None

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