XinBIM NURBS 曲线管理器
一旦来自此扩展的非均匀有理基础样条 (NURBS) 曲线，[均匀有理 B 样条曲线](http://extensions.sketchup.com/en/content/uniform-rational-b-spline-curve “Uniform有理 B 样条曲线”)、贝塞尔曲线([非有理](http://extensions.sketchup.com/en/content/bezier-curve-tool“贝塞尔曲线工具”)或[有理](http:/ /extensions.sketchup.com/en/content/rational-bezier-curve-tool “Rational Bezier Curve Tool”)), freehand curve with up to 20 segments, arc, circle or line is selected, 这个扩展中的工具，演示在上面和下面描述的动画中，可以在“工具”菜单、“鼠标右键上下文菜单”和“NURBS 曲线管理器”下的“视图”>“工具栏”中找到。
当控制点、控制线或曲线本身上的点移动时，所有工具都可以进行推理，并提供有关工具提示推论。此外，移动可以使用 Shift 键进行轴约束。如果按住 Shift 键超过半秒，则约束被解锁。否则，按 Shift 键一次锁定，第二次解锁约束。还显示了锁定方向推理线索（较重的轴颜色）。最后，在移动过程中按 Esc 键会将曲线重置为移动开始前的状态。
**操纵曲线** – 除了通过移动控制点或控制线来编辑选定曲线外，
– 您可以在曲线本身上抓取一个点并为其指定一个新位置，以便新曲线应该通过更改后的位置。这对于可能不喜欢控制点和线的概念并且更喜欢直接操纵曲线上的点的设计师很有用。
– 您还可以通过改变控制点的权重来影响曲线的形状。要明确输入权重，请将光标悬停在 n要更改其权重的端点控制点以绿色突出显示，键入您想要的新权重，不要将光标从控制点移开，然后按 Enter 或 Return。
或者抓取一个用三角形标记的权重点，并将其作为形状参数沿着其控制线移动，以便为您重新计算权重。对于设计师来说，使用这些几何手柄可能比要求输入权重数字更可取。
请注意，更改权重的效果与移动控制点的效果不同。
**操纵结** – 要添加结或增加现有结的多重性，请输入您想要的结值，然后按 Enter 或 Return。您还可以通过在所选曲线上需要打结的位置单击来添加打结。要删除结，请单击您认为不再需要的结。
**Change Degree** – 所选曲线的当前度数显示在 Value Con 中控制箱（VCB）。要更改度数，请键入所需的新值，然后按 Enter 或 Return。
1. 度数提升——在多次修改控制多边形、曲线和权重后，可能会发现 n 度曲线不具备足够的灵活性来模拟所需的形状。该工具允许用户增加所选曲线的阶数，但保持曲线的形状不变。
2. 减少次数——减少曲线的次数将导致曲线转换为具有给定控制点和指定次数的均匀有理基样条曲线。
**更改段数** – 用于显示和表示所选曲线的段数显示在值控制框 (VCB) 中。要调整它，请键入您想要的新值，然后按 Enter 或 Return。
**细分** – 通过选择要细分的点细分所选曲线。您还可以输入要细分的参数值d 按 Enter 或 Return。使用它来生成对于单个曲线来说太复杂而无法处理的形状，或者修剪掉不再需要的曲线部分。
作 者：Jacob S.
Once a Non-Uniform Rational Basis Spline(NURBS) curve from this extension, [Uniform Rational B-Spline Curve](http://extensions.sketchup.com/en/content/uniform-rational-b-spline-curve “Uniform Rational B-Spline Curve”), Bezier curve([non-rational](http://extensions.sketchup.com/en/content/bezier-curve-tool “Bezier Curve Tool”) or [rational](http://extensions.sketchup.com/en/content/rational-bezier-curve-tool “Rational Bezier Curve Tool”)), freehand curve with up to 20 segments, arc, circle or line is selected, the tools in this extension, demonstrated in the animations above and described below, are available under the Tools Menu, in the Right Mouse Button Context Menu and in View > Toolbars under NURBS Curve Manager.
Inferencing is available in all the tools when a control point, control line or point on the curve itself is moved, along with tooltips about the inference. Also, the movement can be axis constrained with the Shift key. If the Shift key is held down for more than half a second, then the constraint is unlocked. Otherwise, pressing Shift once locks and a second time unlocks the constraint. The lock direction inference clue (the heavy, by-axis color) is also shown. Finally, hitting the Esc key during a move will reset the curve to the way it was before the move started.
**Manipulate curve** – Other than editing the selected curve by moving its control points or control lines,
– You can grab a point on the curve itself and designate a new location for it, intending that the new curve should pass through the changed location. This is useful for designers who may not like the concept of control points and lines and would prefer to manipulate points on the curve directly.
– You can also influence the shape of the curve by changing the weights of the control points. To enter weights explicitly, hover the cursor over the non-end control point you want to change the weight of so that it is highlighted in green, type the new weight you want for it, without moving the cursor away from the control point, and press Enter or Return.
Or grab a weight point, marked by triangles, and move it along its control line as a shape parameter to have the weights recomputed for you. It may be preferable for a designer to use these geometric handles rather than requiring inputting numbers for the weights.
Note that the effect of changing a weight is different from that of moving the control point.
**Manipulate Knots** – To add knots or to increase the multiplicity of existing knots, enter the knot value you want and press Enter or Return. You can also add knots by clicking at the locations where you want them on the selected curve. To delete knots, click on the knots you feel are no longer necessary.
**Change Degree** – The current degree of the selected curve is displayed in the Value Control Box(VCB). To change the degree, type the new value you want and press Enter or Return.
1. Degree elevation – After modifying the control polygon, curve and weights a few times, it may turn out that a degree n curve does not possess sufficient flexibility to model the desired shape. This tool lets the user increase the degree of the selected curve, yet leaves the shape of the curve unchanged.
2. Degree reduction – Reducing the degree of the curve will result in the curve being converted into a Uniform Rational Basis Spline curve with the given control points and specified degree.
**Change Number of Segments** – The number of segments used for displaying and representing the selected curve is shown in the Value Control Box(VCB). To adjust it, type the new value you want and press Enter or Return.
**Subdivide** – Subdivide the selected curve by picking the point(s) you want to subdivide it at. You can also enter the parameter value(s) you want to subdivide at and press Enter or Return. Use this to generate shapes that are too complex for a single curve to handle or to trim off parts of the curve you no longer need.
