Modifying a shape so as to constrain it to be through some other entities

A most useful set of powerful constraints is available in the Advanced GSM command, under the Passing Through node in order to enable you to apply a controlled modification to a shape so as to have it through some specified points, curves and surface boundaries or even highlight lines and silhouettes.

The Passing Through drop-down list enables you to set the following constraints.

• Passing Through Points
• Passing Through Curves
• Passing Through Highlights
• Passing Through Section
• Passing Through Silhouette

Passing Through Points

This option enables you to constrain a shape through one or more points just by specifying the Projection type:

Passing Through Curves

This option enables you to constrain a shape through one or more curves just by specifying the Projection type:

Passing Through Highlights

This option enables you to constrain a shape through one or more highlight lines. This method can be particularly useful, as it enables you to proceed as follows:

• Display zebra lines on a shape
• Create silhouette curves accordingly
• Select the view direction properly, so as to have the biggest part of the silhouette curve displayed in the view (anyway, you can control the view direction using the Projection direction options — see below). Then create smoother curves the said silhouettes (zebra lines) should match to improve the shape.
  
• Use the Passing Through Highlights constraint of the Advanced GSM command to apply a controlled modification to the shape so as to have the mentioned silhouettes ( Initial highlight Curve) match the curves you created ( Target highlight). Please note that unless the curve you select as the Initial highlight is of the Curve on Surface type, you will also have to select the surface on which the curve lies ( Support Surface).
  
  
  
  Alternatively, instead of using the initial curve, you can set Initial highlight to Direction so as to define the direction of the silhouette used to compute the initial highlight.
  
• The Projection direction drop-down list enables you to set the direction to be used for the highlight constraint (that is: the direction the highlight must be through) as the one of an existing Line to be selected, the one determined by 2 points to be specified, or simply that of one of the coordinate axes X, Y or Z or Normal to view.

Passing Through Section

This option enables you to constrain the model, or part of it, through a curve obtained as a section of the model itself — which can be created using the Insert Free Hand Curve command.
Please note that with this method the starting curves are automatically selected by the program.

Passing Through Silhouette

The Passing Through Silhouette option enables you to modify the silhouette of a shape.

In the following illustration, the orange curve is a part of the silhouette of the model relative to the view along the X axis. The green curve is the target silhouette to be reached (for example, you might have created it using the Insert Free Hand Curve sketching tool).


 

• The Silhouette item is available in the Passing Through drop-down list. After selecting the surfaces to be modified, select the option. Then you can select the initial silhouette. Two methods are available in the Silhouette type drop-down list:
  • Curve
    Enables you to select only curves of the Curve on Surface type (like the ones you can create using the Light Contour Curve command in the Silhouette mode) and the selected silhouette will be exactly the one you pick.
  • Direction
    Enables you to define the initial silhouette as the one computed following the direction you specify on all the entities to be modified.
    
    

    Note Please take into account that if the entities to be modified are a big number, the computation time can grow considerably. In addition, the computed silhouette can have some discontinuities or can be multiple for a single direction.

    
    The direction of the silhouette can be defined by choosing the corresponding entity in the Silhouette direction drop-down list. The default direction is Normal to view, which takes into account both perspective and orthogonal projection modes.
• When the Silhouette type is set to Curve, a Constraint drop-down list is displayed, so as to enable you to define the constraint:
  
  
  
  

  Target silhouette	To constrain the initial silhouette to match the selected target one.
  Free	No constraints.

• In the Projection type drop-down list you can choose the method to be used to project the initial silhouette onto the target constraint.

  Normal	The initial silhouette will be projected orthogonally onto the target.
  Flat	The initial silhouette will be projected using a linear projection along a specified direction (to be chosen in the Direction drop-down list below).
  Double curvature	The initial silhouette be projected using a spherical projection for which you will have to specify the center.
  Single curvature	The initial silhouette will be projected using a cylindrical projection for which you will have to specify the axis, using the Axis drop-down list below.

  The differences among these types of projection can be best appreciated by looking at the preview of the matching law in the silhouette direction.
  In the model of the images above, if you add preserving curves on the external boundaries of the shape, so as to avoid too big a deformation, you will get the following result:
  
  
   

The Silhouette option has also been added to the Preserving drop-down list, so as to enable you to preserve silhouette curves from the modification.
Also in the preserving case, two methods are available in the Silhouette type drop-down list: Curve and Direction, and the meaning is the same.
In the following illustration, the silhouette curve to be preserved is the orange curve, the same used in the previous example as the initial silhouette.



and the result is the following.



As you can see, the silhouette curve has been preserved successfully.

Try to ...

• Apply a through highlights modification
• Constrain a surface through a curve
• Constrain a surface through a set of points