NURBS Weight

The Edit->NURBS Weight command in the Model module allows you to modify the NURBS curve's shape using the mouse to edit the weight of one or more control points. The modifications in curve shape can vary considerably, depending on whether you reweight one point or several at a time.

By choosing the Edit->Point command, the change is applied to a single point that you pick.

The Edit->Tagged Points command applies changes equally to all tagged points. By tagging points, you can apply the same increment or decrement to more than one point simultaneously. If you tag points in different areas of the curve, the curve changes quite differently than if you tag two points in proximity. The default weight for NURBS control points is 1.0. The minimum weight allowed is 0.001.

The maximum depends on such things as:

• The effect you are trying to achieve. The more extreme the effect, the higher the weight you may need to assign. If you are trying to achieve a sharp point in a circle, you may need to reweight to 1,000.
• The current weight value of the point and its neighbouring points.
• Here's an extreme example: If you are starting with a default circle in which each point has a weight of 1.0, the point can be achieved using a weight of 1,000; if the current weight for all points were already 1,000 (an unlikely situation), you would have to assign a weight of 50,000 to achieve the same point!

You can also choose Edit->Coordinate to edit NURBS weight by entering values in a dialogue box.

Procedure

1. Select a NURBS curve and make sure Show->Point is selected.
2. If you want to apply the same increment/ or decrement to more than one point, tag the points first.
3. Choose the Edit->Point or Tagged Points command, depending on whether or not you have tagged selected points.
4. When editing a single point, you must pick the control point.
   
   When editing tagged points, you can click and drag anywhere in the window.
   
5. Drag the mouse to modify the weight of the point(s):

• Left mouse button allows slow modification
• Middle mouse button allows medium modification
• Right mouse button allows fast modification

If you are reweighting a single point, the status line updates the current weight value of the point. For tagged points, the status line displays the weight increment or decrement.

In all cases, the curve shape is updated interactively in the window.

Last updated 02-apr-1998