
When you draw construction lines and circles, with 2D CoPilot support, the cursor snaps to the existing elements in the viewport and you can use 2D CoPilot features such as
Measure Relative. All construction line commands are supported by the 2D CoPilot. The following construction circle commands are supported by the 2D CoPilot: • Center & Radius • 3 Points • Tangent & Center 
To change from the radius mode to the diameter mode, • Click on the status bar, or, 
When you change from the radius mode to the diameter mode , the following circle commands change: • On the Modeling tab, in the Draw group, the Construction Circle Center & Radius changes to Center & Diameter. • On the Modeling tab, in the Draw group, the Circle Center & Radius changes to Center & Diameter. • On the Modeling tab, in the Modify 2D group, Radius changes to Diameter. 
In the diameter mode, the visual feedback shows the diameter of the circle. To switch to diameter mode, see
Change 2D CoPilot settings. 
• To set the radius of a circle in the radius mode, press SPACEBAR, click on the Option Mini Toolbar (OMT), and type a value for the radius. You can also rightclick somewhere in the viewport, choose Set Radius from the context menu, and type a value for the radius. • To set the diameter of a circle in the diameter mode, press SPACEBAR, click on the Option Mini Toolbar (OMT), and type a value for the diameter. You can also rightclick somewhere in the viewport, choose Set Diameter from the context menu, and type a value for the diameter. 
• As you move the cursor over other 2D elements in the viewport, the 2D CoPilot automatically shows points on the elements where the circle is tangent to those elements. • In the diameter mode, the visual feedback shows the diameter of the circle. To change to the diameter mode, see
Change 2D CoPilot settings. 
When you select the third point of the circle: • To set the radius of a circle in the radius mode, press SPACEBAR, click on the Option Mini Toolbar (OMT), and type a value for the radius. You can also rightclick somewhere in the viewport, choose Set Radius from the context menu, and type a value for the radius. • To set the diameter of a circle in the diameter mode, press SPACEBAR, click on the Option Mini Toolbar (OMT), and type a value for the diameter. You can also rightclick somewhere in the viewport, choose Set Diameter from the context menu, and type a value for the diameter. 
• As you move the cursor over other 2D elements in the viewport, the 2D CoPilot automatically shows points on the elements where the circle is tangent to those elements. • In the diameter mode, the visual feedback shows the diameter of the circle. To change to the diameter mode, see
Change 2D CoPilot settings. 
When you select the second point of the circle: • To set the radius of a circle in the radius mode, press SPACEBAR, click on the Option Mini Toolbar (OMT), and type a value for the radius. You can also rightclick somewhere in the viewport, choose Set Radius from the context menu, and type a value for the radius. • To set the diameter of a circle in the diameter mode, press SPACEBAR, click on the Option Mini Toolbar (OMT), and type a value for the diameter. You can also rightclick somewhere in the viewport, choose Set Diameter from the context menu, and type a value for the diameter. 