Lets you define different segments of NURBS (Non-Uniform Rational B-Spline) curves.
A NURBS curve is characterized by control points and knots. You can change the shape of a curve by moving or editing its control points. Knots are points on a curve or surface where segments join. Unlike control points, knots cannot be interactively manipulated but they are important for a better understanding of curves behavior. In general, the distance between knots is approximated to the distance between the control points.
How to use
1. Click the NURBS curve icon or choose the Tools > Curves > NURBS curve command.
2. The program console prompts Local axes origin.
3. Locate axes origin of the curve following one of the two methods:
a) Click and drag in any view and release the mouse button to confirm placement.
b) Type its XYZ coordinates in the console (values must be separated by a comma, i.e. 1,2,3) and press Enter to confirm. If you press Enter without typing any value in the console, the axes origin of the curve will be placed in relation to the XYZ origin.
4. Successive clicks add control points. You can add points in any view regardless of where you started drawing the curve. If you prefer, you can type exact coordinates from the keyboard. Separate each value with a comma. Your input is immediately displayed in the console. Relative coordinate values can be inserted by typing "@" before numbers (i.e. @2,2,2).
5. Press Spacebar to stop points insertion.
To interactively define the arc hold the mouse button down after the click or click while pressing the Shift key.
Options
XYZ coordinates
To modify XYZ coordinates of a curve point.
Views. Choose the Edit mode. Click the point whose position you want to modify and drag it. Release the mouse button when you reach the desired position.
Modeling Tool panel. Select the point from the scroll list that appears when you click the [. . . ] button. Type the new values in the XYZ data fields and confirm them by pressing Enter.
Remove
To remove a curve point.
Views. Choose the Edit mode. Pick the point you want to remove. Choose the Edit > Delete command.
Modeling Tool panel. Click the [. . . ] button and select the point you want to remove from the scroll list (the views will display it in yellow). Press the Remove button.
Insert
To add new points to a curve.
Views / Modeling Tool panel. Switch on the Insert check button and click in any view. If you have previously selected two adjacent points, you can add points between them.
Order
To set the order of a curve.
Modeling Tool panel. Move the slider or type the value in the Order data field. Press Enter to confirm. Default value is 3. The order of a curve can be modified at any moment.
New Entity
To add a new portion of the curve even with a different order.
Views / Modeling Tool panel. Press the New Entity button and click in any view to add points.
Join
Join can be used for two purposes:
a) To join the start and the end point of the same curve entity.
Views / Modeling Tool panel. Select the end points (see the Selection paragraph for multiple selections) of the same curve and press the Join button. You can then use the Un-join command to unjoin them.
b) To join two end points of two entities belonging to different curves. This operation requires you to work also in the browser in order to combine the two entities by dragging and dropping one curve entity into the other curve. To simply copy the entity, instead of moving it, click and drag it while simultaneously holding down the Ctrl key. Once you have combined the two entities and made them components of the same curve, switch to Edit mode and select the two end points you are interested in joining by either picking them while holding down the Ctrl key or dragging in order to include them in the selection box.
Note: You can obtain the same result by using the Combine command to merge the two curves and then collapsing the Construction Tree.
Un-join
To unjoin two previously joined points.
To break a curve into two pieces at a keypoint.
Views / Modeling Tool panel. Choose Edit mode. Pick the joined points and press the Un-join button. Click the joined points to deselect them. Click again and drag to move the first point. This command can be used in the same way to break a curve obtained with New Entity into two pieces at a keypoint.
Curve Type
To open/close any selected curve.
Modeling Tool panel. Just switch the related radio button on.
Invert direction
To invert the direction or sequence of control points on a curve. Inverting curve directions can be very important when you use modeling tools like Skin and you have curves with different directions.
Modeling Tool panel. Just press the button.
Weight
To adjust the weight of one or more control points of a curve.
Views / Modeling Tool panel. Select the control point or points whose weight factor you want to modify. Move the slider or type the weight factor in the Weight data field. Press Enter to confirm.
Default weight factor is 1. The more you increase this value, the greater the pulling effect that the control point exerts on the curve. Weight factor should not be lower than 0.0001. In fact, 0 is not a valid weight factor. When all control points on a curve have the same weight, the curve is called Non-rational. When control points have different weight factors, the curve is called Rational.
Note: Weight modification should be used very carefully. If you plan to exchange your projects, you should remember that many CAD systems do not support modified weight values. Placing two points close to one another, but not one over the other, grants almost the same result.
See also: