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Arcs

May 20, 2011

An arc is a portion of a circle. The default method for drawing an arc is to specify three points—the start point, a second point, and the endpoint. You can draw arcs using any of the following methods:

•      Three points on an arc

•      Start point center point endpoint

•      Start point center point included angle

•      Start point center point chord length

•      Start point endpoint included angle

•      Start point endpoint starting direction

•      Center point start point endpoint

•      Center point start point included angle

•      Center point start point chord length

•      As a tangent continuation of the previous arc or line

Draw Arcs by Specifying Three Points

You can draw an arc by specifying three points, which are separately the start point of the arc, a point anywhere on the arc and the endpoint of the arc. In the following example, the start point of the arc snaps to the endpoint of a line. The second point of the arc snaps to the middle circle in the illustration.

To draw an arc by specifying three points

1. Choose Draw > Arc> 3 Points.

2. Specify the start point.

3. Specify a second point.

4. Specify the endpoint.

Draw toolbar

Command line ARC

 Start point (A), second point (B), and endpoint (C)

Draw Arcs by Specifying Start, Center, End

Under command line prompts for drawing arc, draw an arc by specifying center, start point and end point.

To draw an arc by specifying its start point, center point, and endpoint

1. Choose Draw > Arc> Start, Center, End.

2. Specify the start point.

3. Specify the center point.

4. Specify the endpoint.

Draw toolbar

Command line ARC

 Start point (A), center point (B), and endpoint (C)

Draw Arcs by Specifying Start, Center, Angle

Under command line prompts for drawing arcs, draw an arc by specifying start point and included angle.

The included angle determines the endpoint of the arc. Use the Start, End, Angle method when you know both endpoints but cannot snap to a center point.

To draw an arc by specifying two points and an included angle

1. Choose Draw > Arc> Start End Angle.

2. Specify the start point.

3. Specify the end point.

4. Specify included angle. To draw an arc in a counterclockwise direction, enter a positive value for the included angle. To draw an arc in a clockwise direction, enter a negative value for the included angle.

Draw toolbar

Command line ARC

 Start point (A), endpoint (B), and included angle (C)

Draw Arcs by Specifying Start, Center, Length

Draw an arc through specifying the center of the arc after picking the start point of arc, then specify the length of arc. Or using center, start, Length either, which is actually equal to specifying included angle.

Draw Arcs by Specifying Start, End, Direction/Radius

Draw an arc through specifying start, end radius/Direction, enter a length or click a line segment using any pointing device either clockwise or counterclockwise. If use the second way, move the cursor to direct the arc upwards or downwards. As the following picture shows, move the cursor downwards to draw an arc up concaved.

Draw Contiguous Arcs and Lines

Immediately after you complete an arc, you can start a line tangent to the arc at an endpoint by way of performing Follow option from the LINE command prompt and pressing ENTER at the Specified First Point prompt. Conversely, if you perform Follow option from the ARC command prompt after you completed a line, you can start an arc tangent to the line at an endpoint.

You can connect sequentially drawn arcs in the same way. To create connected arcs using a menu, click Arc from the Draw menu, and then click Continue. In both cases, the resulting object is tangent to the previous one. You can use the shortcut menu to repeat the Continue option.

To draw an arc tangent to an arc or line

1. Choose Draw > Arc >Continue.

2. Specify the endpoint of the tangent arc.

Draw toolbar

Command line ARC

Endpoint (A)

Commands Reference

ARC: Creates an arc

LINE: Creates straight line segments

OFFSET: Creates concentric circles, parallel lines, and parallel curves

System Variables Reference

ANGDIR: Sets the direction of positive angles

LASTANGLE: Stores the end angle of the last arc entered relative to the XY plane of the current UCS for the current space

WHIPARC: Controls whether the display of circles and arcs is smooth

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