The UCS Icon

by David Watson

Appearance

The UCS icon appears in many different forms, only a few of which are shown below. You may notice, looking at the icons below, that they are all subtly different. Understanding the meaning of these subtle differences can help you to orientate yourself with respect to the current co-ordinate system and in particular, to know where the co-ordinate system origin is located. The captions below each icon describe what it means.

World Co-ordinate System Set to Origin Origin is off screen	World Co-ordinate System Set to Origin Icon displayed at origin	World Co-ordinate System Set to No Origin Origin is on or off screen
User Co-ordinate System Set to Origin Origin is off screen	User Co-ordinate System Set to Origin Icon displayed at origin	User Co-ordinate System Set to No Origin Origin is on or off screen

Probably the most important visual clue is the box that appears at the intersection of the axes. When you see the box, you know that you are working in the World Co-ordinate System (WCS). If you do not see the box, you are working in a User Co-ordinate System (UCS).

You may also sometimes see the icon shown on the right. This is the traditional or 2D UCS icon and was used by versions of AutoCAD prior to 2000i. However, you can still use the old style UCS icons if you prefer (AutoCAD always likes to be backwards compatible). You can also change various other parameters that affect the appearance of the UCS Icon using the commands discussed below.

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UCS Icon Properties

Toolbar	none
Pull-down	ViewDisplayUCS IconProperties…
Keyboard	UCSICON and P for Properties

The UCS Icon properties dialogue box can be used to the appearance of the UCS Icon. The dialogue box is illustrated below and is shown with all values and parameters set to default.

You can choose from 3 different style options, 2D, 3D with cone pointers and 3D without cone pointers. The default is 3D with cone pointers. You can also change the line width. By default, the UCS Icon is displayed using a line width of 1 pixel. Using the drop-down list, you can choose to beef it up a little by selecting a line width of 2 or 3 pixels. The size of the UCS Icon can also be varied. The default size is 15 but you can change the size in a range from 5 up to 95. The values refer to a percentage of your screen height. If you need to, you can also control the colour of the UCS Icon. You can use any of the 255 standard AutoCAD colours. Notice that you can control the colour of both Model Space and Layout UCS Icons separately.

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UCS Icon Settings

Toolbar
Pull-down	ToolsNamed UCS…
Keyboard	UCSMAN

If you want control over whether the UCS Icon is displayed or not (yes, you can turn it off), you will need to use another dialogue box or pull-down menu option. (AutoCAD is often useful but rarely rational!). The UCS Settings tab of the UCS dialogue box can be used to control the visibility of the UCS Icon, whether the icon will appear at the co-ordinate system origin and you can also change these settings for all viewports (assuming you have more than one), or for just the current active viewport.

The UCS dialogue box is illustrated above. As you can see, the options are fairly simple and self explanatory. The settings shown above are the default settings. So, by default, the UCS Icon is On (visible) and it is set to Origin meaning that if the origin of the current co-ordinate system is within the current drawing area and not too close to the edge, the icon will be displayed at the origin point rather than in the lower left corner of the screen. If Origin is turned off (No Origin), the UCS Icon will always be displayed at the lower left position irrespective of the location of the origin point. The All option, to control all viewports simultaneously is turned off by default.

You can also control the On/Off and Origin/No Origin settings from the pull-down menu at ViewDisplayUCS IconOn and ViewDisplayUCS IconOrigin respectively. Notice that these settings are changed when the menu item is clicked. The setting is on when you see the tick against the menu item and off if you see no tick. See the illustration on the right.

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The UCSICON Command

Toolbar	none
Pull-down	none
Keyboard	UCSICON

Finally, for completeness and backwards compatibility, we must mention the UCSICON command. Largely superceded by the commands we have already covered, the UCSICON command can be used to change all the properties and settings described above. This command is one of the old style command line commands but it has been updated to include all the new options. Entering UCSICON at the command line will give the following response:

Enter an option [ON/OFF/All/Noorigin/ORigin/Properties] <ON>:

Simply enter the upper case portion of the option you require. The P for properties option will take you to the UCS Icon properties dialogue box described above.

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