【初学者园地】INSERT中三种SPLINE线有何差别？（0308）

在INSERT---CURVE中
SPLINE、SPLINE BY POLE、SPLINE BY POINTS有何不同？
  
能列举一个以上不同点者得分

没有多大的差别，Spline是一种定义曲线的方法，如何控制该spline 一般有两种简单的方式，一种是让spline通过该点，也就是点在spline线上，这种方法在UG中是Spline By Points，另一种是通过控制Spline的控制点（Pole）来控制spline，除了spline两个端点的控制点在spline上以外都不在spline线上。详情请看《计算机图形学》
ykcaml，可以了给一分了吧？
对了补充一点我就是初学者呀，现在正在学Sketch呢，挺麻烦的呀。

在UG 18中区别大了，:?)
不能得分
INSERT---CURVE

是啊，刚才注意到（我很少用到SPLINE的）。
  
画完之后就可以马上修改了，不用再去编辑，切线和法线方向等看的很清楚！
  
不知道黄点位置的含义是什么，还有那条黄色的线？！　

哦！　还是看HELP好了。。。呵呵。。。
  
  Assign Slope / Curvature
  Opens the Assign Slope / Curvature Mode. Employs a slope handlebar icon tool to let you change the slope and curvature of a spline at a selected point. During spline creation, turning this option on displays a slope handlebar at the currently highlighted (that is, the last created) point handle. Until it is dismissed, splines you create with the Spline by Points dialog will continue to display point handles for newly created or edited splines, and you can use any of those handles with the slope handlebar. If you wish to change the slope or curvature of a preexisting spline, just select the spline to display its point handles, and then select one of the point handles on which to display the slope handlebar.
  
You can drag different controls on the slope handlebar to change the shape of the spline. Controls on the slope handlebar include Move Point, Change Slope, Change Curvature and Change Tangent Magnitude. These controls are depicted as arrowheads and small circles, depending on whether you are in wireframe or shaded mode (see the following figures).
  
Control Handles of the Spline by Points Slope Handlebar (Shaded View Top, Wireframe View Bottom)
  
Only the Move Point control can move a point. The other slope handlebar controls change slope and curvature.
  
Whenever point handles are displayed on a spline, you can use the Assign Slope / Curvature option to click on one, display the slope handlebar, and then change the slope and curvature at that point. Click the Create or Edit Points icon to turn off the slope handlebar.
  
If you display a curvature comb on the curve (Analysis—> Curve—> Combs), the length of the curvature handle is the same length of the curvature comb at the base point. If you change the scale of the curvature comb, the curvature handle length changes accordingly. Grabbing and dragging the curvature handle has the same effect as changing the curvature at the point.
  
Spline Curvature Comb and Slope Handlebar
  
You can also assign slope and curvature by copying it from another object:
  
Display the Slope Handlebar at a point on the spline, and click on the Change Slope or Change Curvature handle. The handle is highlighted (do not drag the handle).
  
Move the cursor over a curve or edge whose slope or curvature you want to match.
  
When the object pre-highlights, a marker displays next to it to signify that the tangent/curvature will be matched with the first selected object.
  
Click on the highlighted object to accept its slope or curvature.
  

SPLINE BY POINTS 方式创建的曲线 点在曲线上;
SPLINE BY POLE   方式创建的曲线 只有开始点和末点在曲线上;端点同上一点的连线就是曲线在端点处的切向
  
Curve on Surface 方式创建的曲线 点在曲线上,并只能是曲面上的点;
  
不能光从词义上理解，结合软件就不同了---BY ykcam1

spline可以作为特征编辑，其他两种不可。

nb-xiao wrote:
spline可以作为特征编辑，其他两种不可。

  
可以编辑！　

idesign wrote:
[quote]nb-xiao wrote:
spline可以作为特征编辑，其他两种不可。

  
可以编辑！　 [/quote]
  
对不起，我正好说反了。
   Creating associative splines is done from the same Spline by Pole or Spline by Points dialog. You can select the associative option, which lets the spline recall its creation method.

可惜我现在处于Windows98下，不知道是否有上述的三个菜单。
Spline中文一般翻译为样条，在Ug中有三种主要方法生成样条：
1 Through Points——生成的样条通过定义的点集
2 By Poles——生成的样条除了首尾两个点，其他的点都不过，所有的点的作用是控制样条的形状，形成控制多边形，这种方法容易控制样条的形状
3 Fit——类似我们读书时做试验的数据统计图标，就是样条尽量接近于给出的点。
Ug描述样条用Nurbs曲线，详细说明讲很长篇，基本上现在的CAD和CG软件都用这种方式，这种曲线用多项式可轻易精确表述。
还有其他的方法，如Conic Curve，Law Curve。
基本上所有的线包括直线和圆弧，都是Nurbs，都可以看成为Spline。