Creating a Mesh  


task target This task shows how to mesh a cloud of points or regenerate an existing mesh.

The Mesh Creation and the Mesh Regeneration actions offer:

  • a neighborhood parameter that makes it possible to fill holes or to let some areas unmeshed,
  • an automatic detection or a manual definition of the meshing plane for the 2D mesher,
  • boundary continuity with contiguous meshes through the Constrained option,
  • a fully automatic 3D meshing (c)INRIA, suitable for mechanical parts
    with blind or through holes, that respects details, especially sharp edges,
  • a sag value to mesh dense clouds with a reduced number of triangles,
    but still respecting the 3D Shape within a given tolerance.


In STL Rapid Prototyping, Mesh Regeneration is allowed on meshes only,
i.e. objects whose partially or totally active cells are meshes.

If this is not the case, a fatal error panel is displayed:
Mesh Regeneration is allowed on meshes only.

aprereq.gif (1231 bytes) Open the Cloud.CATPart model from the samples directory.
  1. Click Mesh Creation or Mesh Regeneration I_CloudTess.gif (1712 bytes).
    The Mesh Creation dialog box is displayed.

  2. Select the Execution Mode option you need:

    • 3D Mesher this is a meshing method for complicated shapes
      (e.g. mechanical objects, clouds that can not be projected onto a single plane,
      or without draft characteristics).
      This is the default option.
      • This mesher provides a Sag option to reduce the number of triangles computed on dense clouds.
        However, this option respects the shape of the object. 
      • You would achieve the same result by filtering the cloud with the adaptative option set
        to the sag value and meshing the output.
      • You can also mesh a cloud with a sag equal to 0. This means that all the points are meshed.
        This algorithm is more suitable to mesh large clouds quickly.
    • 2D Mesher: this is a less complex meshing method, to apply to  simple objects, i.e.
      that can be projected onto a single plane  (smooth shapes).  
      The entry dialog box is replaced with that of the 2D Mesher.
  1. If you have selected the 3D Mesher, if necessary select the sag check box and type its value,
    or keep the default 3D Mesher.

  2. If you have selected the 2D Mesher, select the plane that is the computation reference for the meshing:

    • either one main plane

    • or one defined with the compass

    The quality of the mesh depends on the computation direction.

  1. A Neighborhood value is proposed in accordance with the model.
    This value represents the maximal edge length of the triangles displayed.
    The value proposed is just an approximation of this value.
    Its relevance depends on the distribution of the points in the cloud.
    It is visualized by a sphere. You can change its position by a simple mouse click.

    The sphere is updated when you change the Neighborhood value. 
  1. Select the Display option you need:

    • Triangles to display only the mesh,
    • Shading to simulate the surface of the object:
      • with the Flat option, the light is sent on the triangles along their normal,
      • with the Smooth option, the light is smoothed over the triangles,
        giving a better image of the quality of the surface.
  • Meshing requires a complex computation.
    The computation time will increase according to the size and complexity of your model.
    You may want to filter the cloud before starting the meshing.
  • To mesh large quantities of points, we recommend the following settings:
    • Sag=0mm
    • Triangles not activated
    • Shading activated, with the Smooth option.
These display options are applied within this action only.
Once you have validated the result with OK, the result is displayed in the Smooth mode,
even if the input element or the computed mesh were displayed in another mode. 
  1. Constrained is used to:

    • re-process a portion of a mesh by adding points to an existing mesh or
      reprocessing a meshed cloud that has been unfiltered:
      Open the Mesh2.CATPart model from the from the Samples directory. 
      The original mesh had holes in it. Select a faulty portion and proceed to a new meshing on that portion. 
      The original mesh is in red. The re-processed mesh is in blue. 
    • connect several meshes:
      Open the Mesh1.CATPart model from the Samples directory. Draw two traps on that part and mesh
      them with different values, as shown below. Now activate the remaining square of points, as shown below.
  1. For quicker meshing performances, you can filter portions of the parts according to your successive needs.

    The mesh is unconstrained,  the activation trap does not overlap the previous meshes.
    The resulting mesh is independent from the other two.
    The mesh is constrained, the activation trap overlaps the previous meshes.
    The resulting mesh is connected to the other two.
    Facets of the existing mesh that were totally or partially inside the trap have been removed
    and recomputed to adjust to the additional mesh. 
  2. Click Apply to check or update the result.
    Then click OK to confirm the result and exit the action.
    An element Mesh Creation.x is created in the specification tree.

Increase the Neighborhood value to improve the mesh or reduce it to avoid filling holes that should remain clear:



task target
  • In some cases, it may be difficult  to find a Neighborhood value that will fill unwanted holes, without creating unwanted triangles:
    bt016.gif (14417 bytes) bt017.gif (18149 bytes)
  • Seams may appear on the mesh with the Smooth option, :

  • They indicate that the normals to the facets have different directions at this place. 

  • In 2D and 3D mode, some triangles may overlap and mesh should be corrected.

  • In Constrained mode, they show the common boundaries of meshes.

  • When computing a constrained mesh, type 0 as the Neighborhood value to check the boundaries of the mesh.
    If the boundaries are not satisfactory, modify the mesh plane to improve them.

  • After the computation of a constrained mesh, two mesh elements are visible in the specification tree:
    the constrained mesh and the initial mesh. You can select one and then the other to make sure they are complementary.

  • You can use the Meshes Merge action to obtain a single mesh.

end of task