Defining an Axis System

This task explains how to define a new three-axis system locally. There are three ways of defining it: either by selecting geometry, by entering coordinates or by using a compass.
 

Open the PowerCopyStart1.CATPart document.
 

Create an Axis System from Coordinates

  1. Click Insert > Axis Systems > Axis System from the menu bar.

    The Axis System Definition dialog box is displayed.

    The command automatically computes the parameters for creating the axis system and Default (Computed) is displayed in the Origin and directions fields.

    An axis system is composed of an origin point and three orthogonal axes. For instance, you can start by selecting the vertex as shown to position the origin of the axis system you wish to create. The application then computes the remaining coordinates. Both computed axes are then parallel to those of the current system. The axis system looks like this:
    It can be right or left-handed. This information is displayed within the Axis System Definition dialog box.
    You can choose from different types of axis system:

    • Standard: defined by a point of origin and three orthogonal directions.
      If an axis system is selected before launching the command, the new axis system is a copy of the pre-selected axis system. Moreover, if the compass is attached to the 3D geometry, the new axis system orientations are the same as the compass'. Otherwise, the new axis system orientations are as per the current axis system's.

      Here only the point was selected and nothing specified for the axes.

    • Axis rotation: defined as a standard axis system and a angle computed from a selected reference.

      Here the Y axis was set to the standard axis system Y axis, and a 15 degrees angle was set in relation to an edge parallel to the X axis.

    • Euler angles: defined by three angle values as follows:

      Angle 1= (X, N)

      a rotation about Z transforming vector X into vector N.

      Angle 2= (Z, W)

      a rotation about vector N transforming vector Z into vector W.

      Angle 3= (N, U)

      a rotation about vector W

  2. Select the point as shown to position the origin of the axis system you wish to create. The application then computes the remaining coordinates. Both computed axes are then parallel to those of the current system. The axis system looks like this:

     
    Instead of selecting the geometry to define the origin point, you can use one of the following contextual commands available from the Origin field:
     
    • Create Point: for more information, refer to Points
    • Coordinates: for more information, refer to Points
    • Create Midpoint: the origin point is the midpoint detected by the application after selection of a geometrical element.
    • Create Endpoint: the origin point is the endpoint detected by the application after selection of a geometrical element.

  3. If you are not satisfied with x axis, for instance click the X Axis field and select a line to define a new direction for x axis.

    The x axis becomes collinear with this line.
    • It can be a line created along the surface edge, for example, using the Create Line contextual menu on the selection field, and selecting two surface vertices.
      Similarly you can create points, and planes.
    • You can also select the Rotation... contextual menu, and enter an angle value in the X Axis Rotation dialog box.
     
     

  4. Click the y axis in the geometry to reverse it.

    Checking Reverse next to the Y Axis field reverses its direction too.

  5. You can also define axes through coordinates. Right-click the Z Axis field and select the Coordinates... contextual command. The Z Axis dialog box appears.

  6. Key in X = -1, retain the Y and Z coordinates, and click Close.

    The axis system is modified accordingly, and is now left-handed.
    • If you select one or more directions, the other inputs (directions and origin if not specified) are automatically computed at the end of Axis System Definition command.
    • If you do not select any origin or directions, the system automatically computes them for creating the axis system. When editing the axis system, automatically computed origin or directions fields are filled with Default (Computed). However, there is an associativity between the automatically computed inputs and the user-defined inputs.
    • If one of the inputs to the axis system is deleted externally, the command does not perform automatic computation for rebuilding the axis system. Instead, the axis system update error occurs. If you try to edit this axis system, the command displays No Selection in the field where the input was deleted (origin or directions), and OK  remains disabled till you specify the valid input again.
      You need to edit the axis system features that were created before R23. For this, double-click the axis system in the 3D area or specification tree. The Axis System Definition dialog box appears. Click OK. The axis system is edited.
    • If you would like the command to perform the automatic default computation for an input, select No Selection from the contextual menu of the input and click OK. The command then rebuilds the axis system.

  7. Click More... to display the More... dialog box.

    The first row contains the coordinates of the origin point. The coordinates of X axis are displayed in the second row. The coordinates of Y and Z axis are displayed in the third and fourth row respectively.
    • If no value is selected, the new axis system matches the current one.
    • If the origin is selected, the new axis system origin is set to the origin.
    • The first specified axis defines the corresponding axis of new axis system.
      i.e., if the x-axis is specified by Line.1, then the x-axis of new system is a vector along Line.1.
    • The second specified axis defines the plane between the corresponding first and second axes of the new axis system.
      i.e., if the z-axis is specified by Line.2, then the xz plane is defined by the plane between vectors along Line.1 and Line.2.
    • The third specified axis defines the orientation of the corresponding axis of new axis system.
      i.e., if the y-axis is specified by Line.3, then Line.3 defines which side of the xz plane the y-axis of new system lies.
    • The order of selection of the axes is important: to change the order, select the No Selection contextual item on the appropriate axes.
      For instance, if the axes have been selected in the order x, y, z and you wish to change the order to x, z, y, you must select the No Selection contextual item on y, and select it again.

  8. Uncheck Current if you do not want to set current axis system as the reference. The absolute axis at the bottom right of the document then becomes the current axis system.
      You can specify the desired existing reference axis system in the Axis System box. The specified axis system is now used as a reference for creating the new axis system. When you modify the reference axis system, the created axis system is automatically updated.
    By default, the absolute axis system is selected in this box.

  9. Uncheck Under the Axis Systems node if you do not want the axis system to be created within the Axis system node in the specification tree.

    It will be created either in the current geometrical set or right after the current object in an ordered geometrical set. In this case, the axis system becomes the new current object.
    • This option is persistent and remains active until you modify it again.
    • This option is not stored in the feature.
    • You can right-click the axis system node and select Axis System.x object > Move under Axis Systems to move the axis system under the Axis Systems node.

  10. Click OK.

    The axis system is created.
    When it is set as current, it is highlighted in the specification tree.
    The default size of the axis system is defined in Tools > Options > Infrastructure > Part Infrastructure > Display > Display In Geometry Area > Axis system display size (in mm).
    You can resize the axis system using the manipulators on it. The manipulators appear when you select the axis system, provided that Resize Infinite Elements in the Tools toolbar is turned on.
    You can click Reset resizing to restore the size of the axis system.

  11. Right-click Axis System.1 from the specification tree and select the Axis System.1 object > Set As Current contextual command. Axis System.1 is now current. You can then select one of its plane, to define a sketch plane for example.

    • You can change the location of the axis system and put it in a geometrical set.
      To do so, select it in the specification tree, right-click and select Axis System.1 object > Change Geometrical Set. Choose the destination of the axis system using the drop-down list.
      Refer to the Managing Geometrical Sets chapter to have more information.
    • If you create a point using the coordinates method and an axis system is already defined and set as current, the point's coordinates are defined according to current the axis system. As a consequence, the point's coordinates are not displayed in the specification tree.
    • You can contextually retrieve the current local axis direction.
      Refer to the Stacking Commands chapter to have more information.
    • You can use the Shift key while creating the axis system to select the implicit elements that belong to the axis system.
      Refer to the Selecting Implicit Elements chapter to have more information.
    • There is an associativity between the feature being created and the current local axis system. Therefore when the local axis system is updated after a modification, all features based on the axis direction are updated as well.
    • Local axes are fixed. If you wish to constrain them, you need to isolate them (using Isolate contextual command) before setting constraints otherwise you would obtain over-constrained systems.
    • The display mode of the axes is different depending on whether the three-axis system is right-handed or left-handed and current or not.
      Three-Axis System Current Axis Display Mode
      right-handed  yes solid
      right-handed  no dashed
      left-handed yes dotted
      left-handed no dot-dashed

Create an Axis System using the Compass

  1. Drag the compass onto a 3D model where you want to create an axis system.

  2. Click Insert > Axis Systems > Create axis system from compass from the menu bar.

    The Create axis system from compass command is unavailable till you drag the compass onto a 3D model.

  3. An axis system is created in the tree under the Axis Systems node, respecting the current compass definition.
 

Edit an Axis System
You can edit your axis system by double-clicking it and entering new values in the dialog box that appears. You can also use the compass to edit your axis system. 

Note that editing the geometrical elements selected for defining the axes or the origin point affects the definition of the axis system accordingly.

Right-clicking Axis System.X object in the specification tree lets you access the following contextual commands:

  • Definition...: redefines the axis system.
  • Isolate: sets the axis system apart from the geometry.
  • Set As Current/Set As Not Current: defines whether the axis system is the reference or not.
 
Under the Axis Systems node is not available when editing an axis system.