This section describes how to draw spline curves. Splines are special types of smooth curves that pass through given data points. When you have specified the data points, Creo Elements/Direct Annotation uses a powerful technique (B-spline mathematics) to produce the shape.
Do not attempt to simulate analytic geometry with splines (for example making a straight line or a circle using splines). Use the Straight and Circular commands for this.
To create a spline by interpolation points,
A spline created with interpolation points will pass exactly through the interpolation points used to define it.
When you create a spline with interpolation points, Creo Elements/Direct Annotation automatically determines a control polygon for the spline. You can also draw a spline by specifying these control points.
1. Click Geometry and then, in the Draw group, click the arrow next to Spline.
2. Click Interpolation.
The Interpolation dialog box opens.
3. Specify the first interpolation point for the spline to pass through:
◦ Click the point in the viewport.
◦ Enter its coordinates in the user input line.
4. Continue specifying points as required, using the options (described below) in the menu to guide the spline.
5. Click to complete the operation.
The interpolation menu options
The following options can be selected while building the new spline:
• To specify a different owner for the spline, click Owner on the Interpolation dialog box.
• At any interpolation point, you can specify a tangency condition:
◦ Enter an angle in the box next to Tangent.
◦ Click Tangent and specify a point to indicate the angle.
The spline will leave the interpolation point at the specified angle. To remove a tangency condition, clear the Tangent check box.
• To append the spline to an existing element, click Append to, and select the element. You can append either end of the spline to an element, and Creo Elements/Direct Annotation connects it smoothly.
• For a closed spline, click Closed.
• To undo the last interpolation point specified, click Back.
To create a spline by control points,
When you create a spline with control points, the shape of the spline is influenced by the control polygon formed by the control points. The control polygon can be thought of as a convex hull containing the spline. The spline passes through the begin and end points and is guided by the control points.
To draw a spline by control points,
1. Click Geometry and then, in the Draw group, click the arrow next to Spline.
2. Click Control.
The Control dialog box opens.
3. Specify the first control point to define the shape of the spline:
◦ Click the point in the viewport.
◦ Enter its coordinates in the user input line.
4. Continue specifying points as required, using the options (described below) in the menu to guide the spline.
5. Click to complete the operation.
The control menu options
The following options can be selected while building the new spline:
• To specify a different owner for the spline, click Owner on the Control dialog box.
• For a closed spline, click Closed.
• To undo the last control point specified, click Back.