Layout > Using Layouts for 3D Design > To Create Centerlines, Center Points, and Coordinate Systems
  
To Create Centerlines, Center Points, and Coordinate Systems
1. In a layout, on the Design tab, select one of the following:
Click Centerline and select two points to position the centerline.
Click the arrow next to the Centerline and click Tangent Centerline. Select two points to position the centerline. For each point, select an arc or circle at the point of tangency.
Click Center Point and select a placement point.
 
* To toggle the display of center points, in the Graphics toolbar, click Show center points.
Click Coordinate System and select a placement point.
2. Middle-click to exit the tool.