Performing a Symmetry

This task shows you how to perform various kinds of symmetry on one or more subdivision surfaces.
There are two types of symmetry:
  • no intersection between the subdivision surface and the symmetry plane
  • intersection between the subdivision surface and the symmetry plane.
   
Open the Symmetry1.CATPart document (without intersection) or Symmetry3.CATPart document (with intersection).

  1. Click Symmetry from the Operations toolbar.

  2. From the Tools Palette, click one of the following:

    Option Description  Shortcuts
    Surface Selection Selects a surface. Ctrl+Shift+J
    Plane Selection  Selects a plane. Ctrl+Shift+P
    Plane Manipulation Provides options to manipulate the plane.  


    After clicking Plane Manipulation, new commands appear in the Tools Palette:


    Option Description  Shortcuts
    Define Robot Plane Defines a plane using the subdivision mesh. Ctrl+Shift+C
    Reset Robot Resets the plane. Ctrl+Shift+D
    Reverse side Inverts the side of the symmetry.
    Note: You can also click the arrow in the work area.    		 Ctrl+Shift+I
    No faces cut the symmetry plane Generates a better result when the symmetry plane cuts the faces diagonally. A slider lets you manage the weight of the edges located on the symmetry plane.
    Click to switch to Possible faces cutting symmetry plane .    		 Ctrl+Shift+W
    Sharp to Smooth  Click Sharp to Smooth to switch to Smooth to Sharp .
    This option is available for selection only if  No faces cut the symmetry plane is selected.    		 Ctrl+Shift+H
    Plane Translation Translates the plane. Ctrl+Shift+T
    Plane Rotation Rotates the plane. Ctrl+Shift+R
    Edition Defines the position, angles, dimensions, and weight related to the selected elements. Ctrl+Shift+E
    Attenuation Defines the attenuation for the displacement of the handle. Ctrl+Shift+I
    Symmetry Feature Creates a Subdivision Symmetry.x feature as a result.
    By default, this option is selected.    		 Ctrl+Shift+Z
      Subdivision Feature Creates a Subdivision Surface.x feature as a result. Ctrl+Shift+Q

  3. Select a surface. You can also select multiple surfaces.

    The Plane Selection becomes active.

  4. Select the plane.

    You can also select the plane first then the surface. In this case, the Surface Selection becomes active.
    • No intersection between the subdivision surface and the symmetry plane:
      The result is the mathematical symmetry by a plane:
    • Intersection between the surface and the plane:
       
      In this case, the surface is made of two parts separated by the plane. A side of the surface is automatically chosen, corresponding to the bigger side:
      A new icon appears in the Tools Palette to let you choose the side.
 

  1. In the Modification toolbar, click Multi-selection to select multiple items. Click Multi-selection again when the selection is complete.

  2. Select Side Selection or click in the 3D area to invert the side of the symmetry.

  3. Click to add weight to the intersection (scar) of symmetry. You can also access this command by pressing ALT+SHIFT+H. A click on the attraction type icon modifies its state. The icon has two states:

    • Sharp Attraction: Selecting this gives a sharp edge.
    • Smooth Attraction: Selecting this gives a smooth edge.

    The value of the weight, displayed on the right of the screen can be changed between 0 and 100.

  4. Drag the scale manipulator to add the required weight to the surface.
   
  • Selecting multiple subdivision surfaces with Ctrl or from specification tree, will create multiple subdivision symmetries.

    • The side on which the symmetry instances are obtained, remains same for all the selected surfaces.

    • The weight of sharpness or smoothness remains same for all the selected surfaces.

  • The symmetry keeps the curvature continuity of the subdivision surface, therefore some details of the input mesh will be modified.
  • Previous operations performed on the input surface are also kept.
  • The result of the symmetry is a subdivision surface. Thus, you can perform a symmetry of a symmetry or copy-paste a symmetry or use this feature to associate other subdivision surfaces.
  • The display of the projection plane depends on the option selected for transparency in Tools > Options > Display > Performance tab, Transparency Quality area. The options are:

    • Low (Screen Door)

    • High (Alpha Blending).

    • For more information on these options, see CATIA Infrastructure User's Guide: Customizing: Customizing settings: Performance.
   
  • If the surface is U-shaped, you cannot select a side as it is automatically chosen:
 
  • If the symmetry plane intersects a S-shaped surface, the symmetry cannot be performed.
     Below is an example using the highlighted plane: the symmetry cannot be performed.
    Below is an example using the red highlighted plane: the symmetry can be performed.
 
  • If the face of the surface has only one vertex on the chosen side, the result of the symmetry is a mirror surface.
  • When the symmetry plane cuts the faces diagonally, triangles may be created and the result may not be consistent. Click No Faces cutting Symmetry Plane to generate a better result. A slider appears to manage the weight of the edges located on the symmetry plane.
 

Converting a Symmetry into Subdivision Surface
  To convert a symmetry feature into a subdivision surface, right-click the symmetry in specification tree or geometry and select Convert Into Subdivision. A new subdivision is created.
 

You can also access this command by pressing ALT+SHIFT+C.
 

  • Specification tree as seen with symmetry created:

  • Using the Convert Into Subdivision command on Subdivision Symmetry.1, a new Subdivision Surface.3 is created:
  • All the graphic properties and the material of the symmetry are kept for the new subdivision surface.
  • The Convert Into Subdivision command works for multiple selection also.
  • You can also create a subdivision surface feature as a result instead of a subdivision symmetry feature at the time of symmetry creation by selecting Subdivision Feature  <icon> in the Tools Palette.
   
 

Create a sharp edge
  To create a sharp edge at the symmetry plane, the subdivision surface must intersect the plane and a sharp edge must already exist.