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3D, Autocad, UCS

Understanding UCS (Part 5)

Altough adjusting UCS settings becomes easier with each version or AutoCAD, changing coordinate systems has always been cumbersome. This is why you can call back previous settings within the UCS command and some other sub functions are included in a menu.

You can view this menu by selecting the “Named” option in the UCS command. Even me, who is a command prompt addict is using the UCSMAN command, so it wouldn’t be nice of you to use this menu .

Firstly, let us have the UCS set to another plane just like in the third article.

Figure 1

We usually switch to WCS or another UCS setting after we are done using this UCS. But in order to come back to draw in this plane, we have to do some minor adjustments. We will simply save the UCS settings.

Command: USCMAN

Figure 2

In the UCS managing window (Fig.2), there are three tabs. When you first open the window, the current UCS will be listed as ‘Unnamed‘. By right-clicking it, you can Rename it. I named it as the ‘inclined face‘ in my example. Try to find better names in bigger projects as there will be way more inclined faces. Even better, you should try to find a name that describes the position of the UCS and why you created it. After you are done renaming, ‘Delete‘ option will be added to the right-click menu. ‘Details‘ is the most important item that we have to examine in the right-click menu Fig.3 .

Figure 3

In this window you actually adjust a single component that is described using 4 variables: X, Y, Z coordinates and a unit vector. This 4 variables all depend on the UCS. In this window, you specify the UCS settings that will make use of these variables. Unless you have a very valid reason, all settings should be done using the ‘World‘ plane.

Let’s go back to the previous window. You should select the UCS settings you want to use from the list and hit the ‘Set Current‘ buton to make it the active UCS setting. As you can see, it is very practical to come to this window and save the UCS settings that you will be using frequently. Don’t forget to save the UCS settings as soon as you define them, because you might easily forget if you’re buried in your Project.

In the second tab of the UCS window, there are the ‘Orthographic‘ UCS settings. A new feature among the Orthographic settings is the ‘Depth‘. It is actually the same thing as the ELEVATION parameter in the UCS settings.

Figure 4

It is actually easier to adjust these settings from the command line rahter than using this menu. In AutoCAD 2008 and earlier versions, there is a UCS II toolbar where you can access these settings directly. (Fig.5)

Figure 5

These settings are not included in the ribbon interface in AutoCAD 2009, but as always, there is a way to customize the ribbon interface. Check out the dedicated article: şerit menüsünün özelleştirilmesi (Fig. 6).

Figure 6

Let’s look at the third tab in the UCS window (Fig. 7). You can do the UCS fine tuning here. I will examine the UCS icon settings first:

Figure 7

While working in 3D, especially if we are changing coordinate systems frequently, it is crucial to have the UCS icon in display, in fact I can say that it should be a habit to keep it on. Check ‘Display at UCS origin point‘ if you want the icon to be displayed at the origin. The ‘Apply to all active viewports‘ option applies the settings to all active viewports.

As default, the window comes with the ‘Save UCS with viewport‘ already checked. When this is checked, the USCVP variable is set to 1. It means that the UCS settings will be saved in association with the current viewport. If the UCSVP is set to 0, when you change a viewport, the UCS settings for that window will be activated. The ‘Update view to Plan when UCS is changed’ option is tied up with the UCSFALLOW variable. It updates the view to the Plan view whenver the UCS settings are modified. Most users use the UCS menu to change views, as they are tied up together (UCSFALLOW=1), and they do this without realizing that the UCS also changes with the view. I think the correct way is to have the UCSFALLOW set as 0.

UCS-associated Commands:

UCS: The command we use for changing the UCS. Refer to our articles 1 to 4.

UCSMAN: Displays the UCS manager window. This article explains it in detail.

UCSICON: The command that controls the UCS icon. On/Off (as the name implies..). Use ‘Noorigin’ if you want to keep the icon in the lowe left corner of your display- regardless of the origin. Use ORigin if you want it to be displayed at the origin when the origin is within view, or at the corner if its out of view. With Properties, you can customize your UCS icon.(Fig.

Figure 8

Parameters controlling UCS:

PUCSBASE: The UCS setting name entered here determines the origin point of the orthographic UCS in the paper-space.

UCSBASE: The UCS setting name entered here determines the origin point of the orthographic UCS in the model-space.

UCSFALLOW: The default value is 0. It decides whether the UCS will be changed also whenever the VIEW is changed. I explained it above.

UCSNAME: It is a read-only variable that stores the name of the current UCS settings.

UCSORG: This is also a read-only value that gives you the coordinates of the current UCS, relative to the WCS. The value is stored within the drawing.

UCSORTHO: Very similar to UCSFALLOW. It decides whether the UCS will be changed if you select any of the orthographic UCS settings. (UCSORTHO=1) This should also be watched out for, just like UCSFALLOW. Unexperienced users may not realize that the UCS is changing with the view. This might result in wierdly-inserted blocks and the user might think it is an error. Set the value to 0 to disable this feature.

UCSXDIR: Gives you the X-axis direction of the current UCS as a unit vector. It is associated with the active window. It is embedded within the file and is read-only, very useful for LISP programmers.

UCSYDIR: Gives you the Y-axis direction of the current UCS as a unit vector. It is associated with the active window. It is embedded within the file and is read-only, very useful for LISP programmers.

UCSAXISANG: This is used when you want to rotate the UCS about x,y or z axis and specify the angle of rotation manually. It reads the angle that you specify.

UCSDETECT: Dynamic UCS on (1) or off (0).

UCSVIEW: It controls whether UCS settings are saved (1) or not saved (0) when you are creating a new VIEW. You can also acess it from the VIEW manager window.

UCSVP: Also explained within this article.

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