LESSON 3-12

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THE USER CO-ORDINATE SYSTEM (UCS) When working in 3D, it sometimes necessary to change the plane that you are drawing on. For example, if you need to add some detail to the side of a wall, you would want to draw on that plane. It's like taking a sheet of paper up off the floor (WCS) and taping it onto the wall (UCS). The WCS is the World Co-ordinate System. This is the way that the standard X,Y and Z axis are directed when you begin a new drawing (X to the right, Y pointing up and Z pointing towards you). The UCS is the User Co-ordinate System. This is a ‘redirection' of the WCS based on parameters set by the AutoCAD user. There are several ways of doing this, and we'll look at an example here. This is a simple shape drawn on the WCS with one corner located at 0,0,0. Here is the same object shown a new UCS based on the side of the object, so that you are enabled to draw a rectangle on that side: Notice that the positive X Axis is now pointing along the side of the house. Here's how it was changed: You first choose the 3 point option by typing 3 at the prompt. Next you have to pick three points to define the plane. The first point is the new origin. The second point is where you want the positive X-axis to be positioned. The last point is for the positive Y-Axis. Command: ucs Current ucs name: *NO NAME* Enter an option [New/Move/orthoGraphic/Prev/Restore/Save/Del/Apply/?/World] : 3 Specify new origin point <0,0,0>: (P1) Specify point on positive portion of X-axis <1.0000,7.0000,0.0000>: (P2) Specify point on positive-Y portion of the UCS XY plane <1.0000,7.0000,0.0000>: (P3) This is the ‘3-Point' option of the UCS Command. It is one of the most useful, because you control exactly where the new drawing plane will be. You must also be extremely careful when picking the 3 points, or your plane can be shifted and cause some major problems. I would recommend using this method for most of your UCS work - or at least get very comfortable with it before moving on to other methods. NOTE: Pressing enter immediately after entering the UCS command accepts the default of returning to the WCS. Here are the other options of the UCS command. ORIGIN: Command: UCS Origin/ZAxis/3point/OBject/View/X/Y/Z/Prev/Restore/Save/Del/?/: O Origin point <0,0,0>: This option moves the UCS based on a newly picked origin point. It does not shift the drawing plane at all as you only pick one point. Z-AXIS: Command: ucs Origin/ZAxis/3point/OBject/View/X/Y/Z/Prev/Restore/Save/Del/?/: ZA Origin point <0,0,0>: Point on positive portion of Z-axis <-8.0000,0.0000,1.0000>: This choice allows you to pick two points. First you pick the new origin, then you pick a point for the positive Z-Axis. Make sure you type ZA to choose this option. OBJECT: Command: ucs Origin/ZAxis/3point/OBject/View/X/Y/Z/Prev/Restore/Save/Del/?/: OB Select object to align UCS: Using this method, you have to pick on a 2D object that is lying on a particular drawing plane. This gets tricky, as you have to be aware how your positive X and Y axes end up. VIEW: Command: UCS Origin/ZAxis/3point/OBject/View/X/Y/Z/Prev/Restore/Save/Del/?/: V By choosing the view option, AutoCAD will automatically reset the UCS to be aligned with your current view, keeping the origin where it was previously located. X / Y / Z: Command: UCS Origin/ZAxis/3point/OBject/View/X/Y/Z/Prev/Restore/Save/Del/?/: X Rotation angle about X axis <0>: -90 By selecting either the X, Y or Z options, you need to first pick a point along the axis you have chosen, then provide a rotation angle based on the right hand rule mentioned earlier. PREVIOUS: Command: UCS Origin/ZAxis/3point/OBject/View/X/Y/Z/Prev/Restore/Save/Del/?/: P This option returns you to the last setting you had for the UCS. Restore/Save/Del/?/ The next options are used in conjunction with each other. You have the option of saving a particular UCS with a name. You can then restore that named UCS or delete if you no longer will be using it. Here are examples of these options: Command:UCS Origin/ZAxis/3point/OBject/View/X/Y/Z/Prev/Restore/Save/Del/?/: S ?/Desired UCS name: VIEW1 Command:UCS Origin/ZAxis/3point/OBject/View/X/Y/Z/Prev/Restore/Save/Del/?/: R ?/Name of UCS to restore: view1 Command: UCS Origin/ZAxis/3point/OBject/View/X/Y/Z/Prev/Restore/Save/Del/?/: ? UCS name(s) to list <*>: Current UCS: VIEW1 Saved coordinate systems: VIEW1 Origin = <0.0000,0.0000,0.0000>, X Axis = <1.0000,0.0000,0.0000> Y Axis = <0.0000,1.0000,0.0000>, Z Axis = <0.0000,0.0000,1.0000> Origin/ZAxis/3point/OBject/View/X/Y/Z/Prev/Restore/Save/Del/?/: D UCS name(s) to delete : view1 Deleted 1 UCS name. This was a series where a view was saved, restored, listed, and then deleted. Other notes about the UCS: Be careful when choosing a UCS. Look to the UCS icon and see that it is aligned the way you want it to be. Look for a clean vertical lines if it should be aligned along a vertical plane. Always be aware of where your UCS is located. Make sure that positive X is where you expect it to be.