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Control the User Coordinate System

May 20, 2011

You can use the user coordinate system for convenient coordinate entry and to establish drawing planes.


Control the User Coordinate System (UCS) in 2D

      In ZWCAD, there are two coordinate systems: world coordinate system (WCS) and user coordinate system (UCS). WCS is a fixed coordinate system, where the X axis is horizontal and the Y axis is vertical. The origin (0, 0) is the intersection of the X and Y axes in the lower-left corner of the drawing. You can define a UCS based on a WCS. UCS can be moved, which helps you modify particular sections of your drawing easily. At the same time, you can rotate UCS to specify points in 3D or rotated views. When you rotate UCS, Snap, Grid, and Ortho modes all rotate in line with the new UCS.

      Actually, you enter coordinate value in the current UCS. There are several methods for relocating UCS, shown as follows:

  • Move the UCS by defining a new origin.

  • Align the UCS with an existing object or with the current viewing direction.

  • Rotate the current UCS around any of its axes.

  • Restore a saved UCS.

        You can name a defined UCS and then restore it when needed. The UCS Previous option can reverse up to last 10 coordinate systems in the current session. You can delete a named UCS whenever you do not need it. A UCS can also be restored to coincide with the WCS.


Use World and User Coordinate Systems in 3D

     It is helpful for creating 3D model by controlling the UCS.


Use World and User Coordinate Systems

       In 3D space, there is both a fixed WCS and a movable UCS.

        When you work in 3D, the movable UCS can help you enter coordinate, establish drawing planes, and set views easily. Neither moving nor rotating UCS changes your viewport. The only changes are the orientation and tilt of the coordinate system.

       When you work in 3D, you can simplify the creation of 3D objects by relocating the UCS. To relocate the UCS, change the location of the origin point and the orientation of the XY plane and the Z axis. In 3D space, you can locate and orient a UCS anywhere.

      Only one UCS can be made the current coordinate system at any given time, and all coordinate input and display is relative to the current UCS. If you open multiple viewports, the current UCS applies to all of them. If the system variable UCSVP is on, you can save a UCS along with a viewport, and automatically restoring the UCS each time when you make the viewport current.

        To draw in 3D space, you need to specify X, Y, and Z coordinate value in either the WCS or UCS. The following figure displays the X, Y, and Z axes of the WCS.

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        Generally, the WCS and the UCS are coincident with each other, which means that their axes and origin points are overlapped exactly. No matter how many times you relocate the UCS, you can always use the World option of the UCS command to make it coincident with the WCS.


Control the User Coordinate System in 3D

        You can relocate the UCS by changing the location of the origin point and the orientation of the XY plane and the Z axis. In 3D space, you can locate and orient a UCS anywhere. In addition, you can define, save, and recall as many UCSs as you like. Both entering coordinate and drawing are processed in the current UCS.

       With the UCS's relocation, you can acquire the exact placement of a 3D point by aligning the coordinate system with existing geometry.

        In the current session, if multiple viewports are active, you can assign a different UCS to each viewport. If the system variable UCSVP is on, you can save a UCS along with a viewport, and automatically restoring the UCS each time when you make the viewport current. When the system variable UCSVP is on, each UCS may have a different origin and orientation dependent on the construction.


Define the UCS Location

 You can define a UCS in several ways:

  • Specify a new origin, new XY plane, or new Z axis.

  • Align the new UCS with an existing object.

  • Align the new UCS with the current viewing direction.

  • Rotate the current UCS around any of its axes.

  • Apply a new Z-depth to an existing UCS.

  • Apply a UCS by selecting a face.


Use UCS Presets

On the Orthographic UCS tab of the UCS dialog box, the system lists several preset coordinate system, from which you can choose the desired one.

After specifying a UCS, you can control whether choosing a preset option shifts the UCS relative to the current UCS orientation or relative to the default WCS. If you use the Restore, World, or Previous option of the UCS command, the settings you made are not available.


Change the Default Elevation

        The ELEV command is used to specify an elevation and thickness of extrusion for a new object. You can define a drawing plane of the current UCS by establishing the current elevation, which can be applied to individual viewports in conjunction with the system variable UCSVP. Whether a UCS is saved or restored in each viewport are determined by this variable. When UCSVP is set to 1, the different UCS settings are saved in individual viewports, and the elevation settings are saved along with each viewport both in model space and in paper space layouts.

        Generally, the elevation is set to 0, and you can control the XY plane of the current UCS using UCS command.


Change the UCS in Paper Space

       Just as you define a new UCS in model space, you can also define a new UCS in paper space; however, the UCSs in paper space are only available for 2D manipulation. Although you can enter 3D coordinates in paper space, 3D viewing commands are not available, such as DVIEW, PLAN, and VPOINT.

       The system can store the last 10 coordinate systems that were created in model space and the last 10 in paper space, and you can restore to the desired one using the Previous option of the UCS command.


Save and Restore UCS Locations by Name

       You can save named UCS locations, each having a different origin and orientation, for various construction requirements. You can relocate, save, and recall as many UCS orientations as you require.


Assign User Coordinate System Orientations to Viewports

      You can create multiple viewports to display different views of your model. For example, you can specify top, front, right side, and isometric views for viewports. You can also define a different UCS for each view to facilitate modifying objects in different views. When you make a viewport current, you can use the same UCS you used the last time that the viewport was current.

      The system variable UCSVP controls the UCS in each viewport. When UCSVP is on in a viewport, the system saves the viewport with the UCS last used in that viewport and restores the UCS as the viewport is made current again. When UCSVP is set to 0 in a viewport, its UCS is coincident with the UCS in the current viewport.

        For example, you can set up three viewports: a top view, front view, and isometric view. If UCSVP is set to 0 in the isometric viewport, the Top UCS can be applied to both the top viewport and the isometric viewport. When the top viewport is made current, the isometric viewport's UCS reflects the UCS top viewport. Likewise, if you make the front viewport current, the isometric viewport's UCS is switched to match that of the front viewport.

         The following figure indicates the instance illustrated above. In which the drawing 1 reflects isometric viewport of top-left or top viewports in current UCS.

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       The second figure shows the change that occurs when the lower-left, or front, viewport is made current. The UCS in the isometric viewport is updated to reflect the UCS of the front viewport.

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Control the Display of the User Coordinate System Icon

        By default, the UCS icon is displayed in the lower-left corner of the current viewport, which indicates the location and orientation of the current UCS. You can also control whether the UCS icon is displayed at the origin point. There are two types of UCS icons: 2D icon and 3D icon.

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        Displaying 2D or 3D UCS icon is controlled by the UCSICON command. You can display the UCS icon at the UCS origin point to indicate the origin and orientation of the current UCS using the UCSICON command.

     A cross is displayed in the icon if the UCS icon is displayed at the corner of the current UCS; otherwise, there is no cross in the icon.

       If the drawing area has multiple viewports, each viewport displays its own UCS icon.

       There are various ways for displaying the UCS icon, shown as follows, which help you visualize the orientation of the drawing plane.

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The UCSICON can also change the size and color of the UCS icon.


Commands Reference

UCS: Manages user coordinate systems

UCSICON: Manages user coordinate systems

UCSMAN: Manages defined user coordinate systems

System Variables Reference

ERRNO: Displays the number of the appropriate error code when an AutoLISP function call causes an error that ZWCAD detects

PUCSBASE: Stores the name of the UCS that defines the origin and orientation of orthographic UCS settings in paper space only

UCSFOLLOW: Generates a plan view whenever you change from one UCS to another

UCSNAME: Stores the name of the current coordinate system for the current viewport in the current space

UCSORG: Stores the origin point of the current coordinate system for the current viewport in the current space

UCSXDIR: Stores the X direction of the current UCS for the current viewport in the current space

UCSYDIR: Stores the Y direction of the current UCS for the current viewport in the current space

UCSICON: Displays the UCS icon for the current viewport using bitcode

UCSVP: Determines whether the UCS in active viewports remains fixed or changes to reflect the UCS of the currently active viewport


 

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