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Coordinate System

May 20, 2011

      Many commands in ZWCAD require that you specify points as you draw or modify entities.

      You can do so by selecting points with the mouse or by typing coordinate values in the command bar. The program locates points in a drawing using a Cartesian coordinate system.

Understanding how coordinate systems work

       The Cartesian coordinate system uses three perpendicular axes—x, y, and z—to specify points in three dimensional space. Every location in a drawing can be represented as a point relative to a 0,0,0 coordinate point, referred to as the origin. To draw a two dimensional entity, you specify horizontal coordinate positions along the x axis and vertical coordinate positions along the y axis. Thus, every point on a plane can be represented as a coordinate pair composed of an x coordinate and a y coordinate. Positive coordinates are located above and to the right of the origin; negative coordinates are located to the left and below the origin.



The three perpendicular axes of the Cartesian coordinate system

       When you work in two dimensions, you need enter only the x and y coordinates; the program assumes that the z axis value is always the current elevation. When you work in three dimensions, however, you must also specify the z axis value. When you look at a plan view of your drawing (a view from above, looking down), the z axis extends straight up out of the screen at a 90 degree angle to the xy plane. Positive coordinates are located above the xy plane, and negative coordinates are below the plane.

        All ZWCAD drawings use a fixed coordinate system, called the World Coordinate System (WCS), and every point in a drawing has a specific x,y,z coordinate in the WCS. You can also define arbitrary coordinate systems located anywhere in three dimensional space. These are called user coordinate systems and can be located anywhere in the WCS and oriented in any direction.

        You can create as many user coordinate systems as you want, saving or redefining them to help you construct three dimensional entities. By defining a UCS within the WCS, you can simplify the creation of most three dimensional entities into combinations of two dimensional entities.

       To help you keep your bearings in the current coordinate system, the program displays a coordinate system icon. When you begin a new drawing, you are automatically in the WCS, indicated by the letter W in the icon. When you display a drawing in plan view, you see the coordinate system icon from the top, with the z axis directed straight toward you. When you display a three dimensional drawing in a view other than plan view, the coordinate system icon changes to reflect your new viewpoint.

TIP The visible portions of the axes are the positive directions.



WCS icon Plan UCS icon 3D View WCS icon

Understanding how coordinates are displayed

       The current position of the cursor is displayed as x,y,z coordinates in the status bar and, by default, updates dynamically as you move the cursor. You can toggle the coordinate display to static mode by pressing F6, so that it updates only when you select a point in the drawing.

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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