UCS Command

In AutoCAD, you are in top view and that is your XY plane. You cannot draw in any other plane other than XY plane. Therefore, while working in 3D, you need to change your UCS a number of times to draw on different planes/faces of your model.

        So, here you are going to learn about the various options available within UCS command which is used to move, align, rotate, etc. your UCS.

UCS Command

Various options available in UCS Command :

If you choose the default option, you can establish a new coordinate sysytem by specifying a new origin point ; a point on positive x-axis and a point on Y-axis and the direction of Z-axis is determined using right hand thumb rule.

1. Face :

This option lets you define a new UCS aligned with a selected face of a model(solid,surface or mesh).

You can also do so by selecting the face option from the align UCS drop down as shown above.

The command prompt first prompts you to directly to select the face of solid, surface, or mesh to align the new UCS with. Then it prompts you to define the following option :

i). Next : 

This option is used to locate the new UCS on the adjacent face or the back face of the selected face.

ii). Xflip/Yflip :

These are used to rotate the new UCS by 180⁰ around the respective axis as chosen. 

The default option is accept  which lets you apply the face selected as the new UCS.

2. OBject :

With this option, you can define a new UCS by selecting an object in your drawing such as a circle, arc, line, etc.However, some of the objects including 3D pline,3D mesh, viewport object, xline, etc. cannot be used to define a new UCS. 

         You can also invoke this option fro the Align UCS drop down as shown above. The direction of positive Z-axis is same as that of the object selected. If the X and Z axes are known, then the direction of Y-axis can be determined using right hand thumb rule. But the question arises what will be the origin of such a new UCS. Here is the origin point for different objects selected :

i). Arc/Circle/Ellipse/Cylinder :

In these cases, their center becomes the origin point of new UCS.

ii). Line :

The new UCS origin is the endpoint of the line nearest to the point at which you specified. The X-axis is defined so that the line lies in XY plane.

3. View :

The view option of the UCS command is used o define a new UCS whose XY palne is parallel to the current viewing plane. The current viewing plane is the monitor of the screen. Therefore, a new UCS is defined that is parallel to the screen of the  monitor. The origin of the UCS defined using this option remains unaltered.

        

           You can also invoke this option using the  Align UCS drop down as shown above.

4. X/Y/Z :

With these options, you can rotate the the current UCS around the desired axis, You can specify the angle at the required prompt or by selecting two points on the screen. The angle is taken relative to the X-axis of the current active UCS. 

   

           You can also invoke this option using the Rotate UCS drop down available within the coordinates panel of the home tab.

 You can also directly manipulate the UCS to define a new UCS by selecting the UCS and then right click to get the shortcut menu and then selecting the Rotate option.

5. Previous :

The previous option is used to restore the current UCS settings to the previous UCS settings. AutoCAD saves the last ten UCS settings.

 6. World :

This option is used to set the UCS to World Coordinate System(WCS). The origin of WCS is fixed to 0,0,0 and the home view is set to South-West Isometric.

7. Origin :

This option is not available within the UCS command but you can invoke this option using Coordinates panel. This option is used to define a new UCS by changing the origin of the current UCS, without changing the direction of the axes.