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Jaiprakash Pandey posted on November 25, 2016 |

Understanding coordinate systems is crucial for working with 3D models in AutoCAD. In AutoCAD, all 2D geometries are drawn on the XY plane. To draw on any other plane, you need to rotate the user coordinate system (UCS) to that direction.

Coordinates panel on the home tab.

The importance of coordinates in AutoCAD is evident from the fact that a complete Coordinates panel is dedicated to tools for manipulating the UCS. To explain the tools of the Coordinates panel, I will use a simple geometry as shown in Figure 1.

Figure 1. Sample geometry with different planes indicated with different colors.

### Aligning the UCS to Any Plane with Reference to Objects

In Figure 1, the blue plane is perpendicular to the existing plane, as shown by the UCS in the lower-left corner. To change the UCS to align with the blue plane, select the Face option from the View drop-down menu in the Coordinates panel. Click the face on which you want to align the UCS and press Enter. You will notice that your UCS will align to that plane.

You can also use the three-point UCS option for aligning it to any plane. The red plane is neither horizontal nor vertical with respect to the current UCS and it is aligned at an unknown angle. In order to align the UCS with respect to the red plane, select the three-point tool and click on any vertex of the plane. Now, specify the X axis by clicking at any second point along the edge of the plane. Then, specify the Y axis by clicking at another point along the edge of the plane. You will notice that the Z axis will align itself with respect to the assigned axes, as shown in Figure 2.

Figure 2. UCS aligned with the red plane of the 3D object.

### Making a Drawing on Parallel Planes

When you draw an object, it will always be done on the current XY plane. If you want an object to be drawn on a plane parallel to an existing plane but at a certain distance from it, then you need to move your plane to that distance along the Z axis. To move the UCS so that the orientation of the XYZ axes remains unchanged, select the Origin tool from the Coordinates panel and click at a point along the Z axis. The point where you click will become the new origin and the UCS will align itself parallel to the previous plane at the new point.

### Aligning the UCS with Respect to 2D Objects

You can also align the UCS with respect to a 2D object like a polyline or a circle. Let’s say that we have a drawing in which several 2D objects are made on different planes. In order to make a new object on the same plane on which any existing 2D object is made, we need to first change the orientation of our UCS to that of the object. To do that, select the Object tool from the View drop-down menu in the Coordinates panel and click on the 2D object with which you want to align the coordinates. You will notice that your UCS will align to the new configuration and now you can make drawings on the plane of the selected objects.

There are also circumstances when you only have the Z axis vector of the 2D object and you want to make an object on a plane that is perpendicular to that Z axis. For these cases, you can use the Z-axis vector tool in the coordinates panel. I will explain this with the help of a simple example shown in Figure 3.

Figure 3. Lines aligned to an unknown angle with respect to each other.

Here we have two lines inclined at an angle with each other. If we want to make a circle in such a way that the center of the circle lies at the endpoint of the line (and it follows the path of the line when extruded), then we need to align the UCS with respect to these lines. Select the Z-axis vector tool from the Coordinates panel, click at any one of the end points of the line and click again at the next endpoint. Now you can draw the circle at the end of the line and the end result will look like Figure 4.

Figure 4. The XY plane aligned to the perpendicular direction with respect to one of the line segments.

### Moving the UCS to Predefined Configurations

When you look at the view cube on the top-right side of the drawing window, you will notice that it has six faces. You can align the UCS to make the XY plane parallel to any of these planes using the World drop-down menu in the Coordinates panel. As an example, to align the XY plane of the UCS with respect to the right view, select Right from World drop-down menu. You will notice that the right view of the UCS changes to the top view and that it is also parallel to the XY plane.

So far, we have changed the orientation of the UCS multiple times. At any point in time, if you want to return to the previous state of the UCS, click on the Previous tool in the Coordinates panel. If you want to reset the UCS to the default condition or to the world coordinate system (WCS), click on the World icon in the Coordinates panel.

### Changing Properties of the UCS

The default UCS in the AutoCAD 3D workspace will show three mutually perpendicular axes represented by X (red), Y (green) and Z (blue). You can change the position and shape of the UCS using the Properties menu. Click on the Properties icon in the Coordinates panel and a new UCS icon window will pop up as shown in Figure 5. Alternatively, you can also right click on the UCS and select Properties from the UCS icon settings submenu in the contextual menu.

Figure 5. UCS icon properties window.

From this window, you can change the UCS icon style to 2D or 3D and you can also change the line width of the UCS icon from the UCS icon style panel. By default, the color of the UCS icon will remain white in the wireframe visual style of the model space, but you can change its color as well using the Color drop-down menu in the UCS icon color panel. In a similar way, the color of the UCS icon in the layout view can also be changed from the layout color tab.

### Dynamic UCS

So far, we have used a method of changing a plane in a drawing using the tools in the Coordinates panel, but there is one more method of creating geometries on a desirable plane by taking reference of existing 3D geometries. This method is called dynamic UCS. In order to use the dynamic UCS, click on its icon on the status bar. Alternatively, you can press F6 to activate the dynamic UCS option.

Figure 6. Dynamic UCS icon on the status bar.

Once the dynamic UCS is active, you will see the icon highlighted, as shown in Figure 6. If you are not able to find the dynamic UCS icon on the status bar, click on the Customize icon on the far-right side of the status bar and select the dynamic UCS from the menu.

For the dynamic UCS to work, you need to have a 3D geometry in the drawing area. To start working with the dynamic UCS, select the 2D Draw command that you want to use and then go to the plane on which you want to place the object. You will notice that the plane becomes highlighted and the UCS will also change temporarily to show the selected plane as the XY plane. Click at the point on the plane and make your 2D drawing.

This process of making geometries on 3D objects is easier compared with the methods shown above, but it has a limitation. You need to have a reference 3D geometry and a plane for making the 3D curve. As soon as the cursor moves beyond the plane, the UCS will reorient itself to the default value selected and the object will not be drawn on the desired plane.

### Conclusion

The methods shown above are most frequently used for manipulating UCS. Generally, you will use a combination of these methods to get the desired UCS orientation for making geometries. For a novice user, using coordinates can be an intimidating topic, but with practice, you will become really good at using the UCS.

Do you have questions related to this tip? Let us know in the comments below.

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