Draft Arc/zh-cn

描述
底图绘弧工具通过用户输入的4个点（圆的中心点、半径、第一个点与最后一个点），或通过拾取切线，或上述若干组合来在当前的work plane上创建一个圆弧. 它将根据Draft Tray中的Draft Linestyle来创建圆弧.

除了添加起始角度与终止角度这两个参数之外，本工具的工作方式与底图圆形工具相同. 要绘制椭圆弧，可借助底图椭圆工具. 另外，您也可以通过底图B样条与底图贝叶斯曲线工具来近似地逼近一条圆弧.



如何使用

 * 1) 按下按钮，或先按键再按键.
 * 2) 在3D视图中点击第一个点，或输入一个 坐标并按按钮.
 * 3) 在3D视图中点击第二个点，或输入一个半径值.
 * 4) 在3D视图中点击第三个点，或输入一个起始角度.
 * 5) 在3D视图中点击第四个点，或输入一个张角.

The arc can be edited by double clicking on the element in the tree view, or by pressing the button. Then you can move the center point to a new position.

The arc can be turned into a circle after creation, by setting its first angle and last angle properties to the same value.

Options

 * The primary use of the arc tool is by picking four points: the centre, a point on the circumference, the start of the arc, and its end.
 * By pressing, you can select a tangent instead of picking point, to define the base circle of the arc. You can therefore construct several types of circles by selecting one, two or three tangents.
 * The direction of the arc depends on the movement you are doing with your mouse. If you start to move clockwise after the third point is entered, your arc will go clockwise. To go counter-clockwise, simply move your mouse back over the third point, until the arc starts drawing in the other direction.
 * To enter coordinates manually, simply enter the numbers, then press between each X, Y and Z component. You can press the  button when you have the desired values to insert the point.
 * Press or click the checkbox to toggle continue mode. If continue mode is on, the Arc tool will restart after you finish the arc, allowing you to draw another one without pressing the tool button again.
 * Hold while drawing to force snapping your point to the nearest snap location, independently of the distance.
 * Hold while drawing to constrain your point horizontally or vertically in relation to the center.
 * Press or the  button to abort the current command.

Properties
An Arc object shares all properties from a Draft Circle, but some properties only make sense for the circle.

Data

 * : specifies the angle of the first point of the arc.
 * : specifies the angle of the last point of the arc.
 * : specifies the radius of the arc.
 * : specifies if the arc makes a face or not. This property only works if the shape is a full circle.
 * To make an arc a full circle set the and  to the same value. The values 0&#176; and 360&#176; aren't considered the same, so if these two values are used, the circle will not form a face.

View

 * : specifies a Draft Pattern with which to fill the face of the arc. This property only works if the arc is a full circle, and if is, and if  is "Flat Lines".
 * : specifies the size of the Draft Pattern.

Scripting
Draft API and FreeCAD Scripting Basics.

The Arc tool can be used in macros and from the Python console by using the same function to create circles, with additional arguments. See the information in Draft Circle.

Example: