Creating a Surface Automatically from a Mesh

You can create surfaces automatically from a mesh, as standard features, and then convert them into Imagine & Shape features.

Automatic Surface is adapted to many types of shapes.

  • It can create complex surfaces with a minimum set of Nurbs.
  • It can take holes into account.
  • It preserves fillet with small radius (but not very sharp edges).
  • You can choose the type of stream lines, and add your own constraints.

This task shows you how to:

Before you begin: The input required is a mesh (not a cloud of points):
  • It may not have non-manifold vertices or triangles,
  • It must be a mono-cell mesh, without non-connex zones.

Set the Options

You can specify a Mean surface deviation and a Surface detail for all cases, and decide of the quality of the stream lines.

  1. From the Surface Reconstruction section of the action bar, click Automatic Surface and select a Mesh.
    • The name of the mesh you have selected is displayed in the dialog box.
    • is now available to hide or show the mesh.
    • You can edit parameters values and select check boxes according to your needs.
  2. Decide if you want to create the surface with:
  3. Key in the Mean surface deviation, that is, the average deviation between the surface to create and the input mesh, computed on all mesh vertices.
  4. Key in a Surface detail value: The higher the value, the higher the respect of details.
  5. Optional: When the check box is editable and not required, clear the Full internal tangency check box.

    Warning: Full internal tangency cannot be retrieved later on, for example with healing or filleting commands. Nor can you perform thickness or offset operations on the output surface.

    When Full internal tangency is not selected, the output is smaller in term of memory size and control points.
  6. Click Apply to compute the surface.
    Statistics on the created surface are now available.
  7. Click OK.
    A feature Automatic Surface.x is created.
  8. Right-click the Automatic Surface.x feature in the tree and select Convert Into Subdivision.

    Note: Convert Into Subdivision is not available if the Automatic Surface.x has been created with Regular stream lines without Extend surface.

    An Imagine & Shape Subdivision Surface.x feature is created.

Create Surfaces with Regular Stream Lines

You can request regular stream lines for a regular and smooth output.

Note: When the Regular stream lines check box is selected, a valid, but untrimmed surface may be created instead of the expected trimmed one. An information message is displayed.

  1. Select the Regular stream lines check box.

    By default:

    • The check box Regular stream lines is selected. Constrained stream lines check box is not.
    • The check boxes Free edge tolerance, Full internal tangency, and Dynamic preview are also selected and taken into account, but are not editable while Regular stream lines is selected.
    • Target ratio is not editable.
    • The check boxes Fill holes and Extend surface are available but not selected.
      Note: Regular Stream Lines, Fill holes and Extend surface are not available for closed meshes.

  2. Optional: Select the Fill holes check box.
    • Fill Holes is not selected:

    • Fill Holes is selected:

  3. Optional: Select the Extend surface check box and adjust the extension with the slider.

    By default, Extend surface is not selected. The output surface is trimmed on the external and internal free edges of the mesh.

    • Extend surface is not selected:

    • Extend surface is selected:

  4. Click Apply and go to Display Statistics

Create Surfaces with Constrained Stream Lines

You can apply your own constraints to manage the stream lines.

  1. Select the Constrained stream lines check box.

    • The check boxes Free edge tolerance and Dynamic preview become editable.
    • The check box Full internal tangency is selected and taken into account, but not editable.
    • The check box Fill holes is available but not selected.
    • The check box Extend surface is no longer available.

  2. Pick a point on the mesh, and use the context toolbar to create your constraints.
    1. Click and pick a point to create a constraint point.
    2. Click and pick two points to create a constraint line.

    3. Click and pick a free edge to create a constraint on the whole free edge.

    4. Click to delete a constraint or a stream line.
  3. Click Preview.
    The stream lines are computed and displayed:

    • Automatically computed constraint and the constraints you have specified (in yellow), iso stream lines (in blue) and gradient stream lines (in red).
    • Gradient stream lines are perpendicular to the constraints, when iso stream lines are turning around constraints.
    • Constrains can be points or lines.
    • Examples:
      • Constraint point in yellow, iso stream lines in blue, gradient stream lines in red:

      • Constraints lines in yellow, iso stream lines in blue, gradient stream lines in red:



  4. Use the context toolbar to modify the stream lines
    1. Click , or to add an iso stream line, a gradient stream line or both.
    2. Drag and drop a stream line to move it.
  5. To see the results of your modifications, either click Preview after each interaction, or select the Dynamic preview check box.
  6. Click Apply and go to Display Statistics

Create Surfaces with Any Stream Lines

You can clear the Regular Stream Lines and the Constrained stream lines check boxes. Stream lines in the output are less regular.

  1. Clear the Regular stream lines or Constrained stream lines check boxes.

    • The check boxes Fill holes and Extend surface are no longer available.
    • The Free edge tolerance and Full internal tangency check boxes are editable. The value of Free edge tolerance can be edited.
    • Target ratio becomes editable.

  2. Select or clear the Free edge tolerance check box that is, the chordal value used to sample the mesh boundaries and to improve the quality of the surface with respect to the mesh boundaries.
    • Free edge tolerance is not selected:

    • Free edge tolerance is selected:

  3. Key in a Target ratio: Ratio of measured points with a surface deviation under the Mean surface deviation value. The actual ratio obtained may be different (greater or lower) than the one you have requested.

    Important:
    • A target ratio next to 100 is time consuming.
    • If the mean surface deviation or the target ratio requested cannot be reached, the surface is created and a message is displayed.

Display Statistics

You can display statistics on the created surface once you have clicked Apply.

  1. Click More to access the statistics and some display check boxes.

    The Statistics are:

    • output faces: Global count of faces contained in the output surface.
    • Max surface deviation: Value of the maximum deviation between the surface and the mesh, also displayed with the spikes.
    • Max free edges deviation: Value of the maximum deviation between the free edges and the mesh, also displayed with the spikes.
    • Mean surface deviation: Value of the mean deviation between the surface and the mesh.
    • xx% of yyy points Ok: Percentage of the measured points that are under the Mean surface deviation.

    Notes:
    • Automatic Surface generates the output surface from an approximation computation. The statistics, spikes, and deviation information displayed within Automatic Surface result from the same approximation and are meant to define and adjust the surface parameters.
    • Should you require more accurate deviation results, perform a deviation analysis once the automatic surface has been generated.

  2. Select the Spikes check box to display the deviations between the mesh and the surface.
    • The points with the maximum deviation on the surface or on free edges are displayed on a small yellow rectangle, with the corresponding value of the deviation.
    • Deviation enables you to display only the spikes on points with a deviation greater than this value.
    • Negative and positive deviations are displayed in different colors.
  3. Select to display the deviations on the surface.
  4. Select to display the deviations on the free edges (only available when free edges exist).