Extracting Geometry

This task shows how to perform an extract from elements (curves, points, surfaces, solids, volumes and so forth).

This may be especially useful when a generated element is composed of several non-connex sub-elements. Using the extract capability
you can generate separate elements from these sub-elements, without deleting the initial element.

Open the Extract1.CATPart document.

 

  1. Click Extract .

    The Extract Definition dialog box appears as well as the Tools Palette.
    For further information about the Tools Palette, refer to Selecting Using Selection Traps in the CATIA Infrastructure User's Guide.
    In the Part Design workbench, the Extract capability is available as a contextual command named Create Extract that you can
    access from Sketch-based features dialog boxes.

  2. Select an edge or the face of an element.

    The selected element is highlighted.
    Multi-selection is available to let you select several elements to be extracted.

  3. Choose the Propagation type: 

    • Point continuity: the extracted element will not have a hole.
    • Tangent continuity: the extracted element will be created according to tangency conditions. 
    • Curvature continuity: the extracted element (necessarily a curve) will be created according to curvature conditions.
    • Depression/Protrusion propagation: Protrusions and/or depressions of a surface can be selected quickly. Also, the base surface can be selected without its protrusions and/or depressions. Two cells belong to a protrusion if their union is convex. Two cells belong to a depression if their union is concave.
       
      A cell belonging to the Extract Feature's result is selected (green). A neighboring cell (orange border) is smoothly connected to it through a constant fillet.   Both cells belong to a protrusion: neighboring cell and fillet are added to the Extract Feature's result.  The same applies to the second neighboring cell. 
       
      •  Depression/Protrusion propagation modes are only available if the element to extract is a surface.
      • Please note that the computation with protrusion or depression propagation takes more time than with another propagation type.
    • No propagation: only the selected element will be created.
      If either Intersection edges activation or Tangent Intersection edges activation icon is selected in the User Selection Filter
      toolbar before launching the Extract command, then the Geometrical Element Filter icon is automatically activated and the Propagation type set in the Extract Definition dialog box is applied.
      Deactivate the Geometrical Element Filter icon to take into account the behavior of the Intersection edges activation or
      Tangent Intersection edges activation       capability.
      When you click OK in the Extract Definition dialog box, the status of the Geometrical Element Filter icon returns to normal.

  4. If one of the propagation types Depression/Protrusion propagation is selected, the set Recognition context is considered while propagating the selection.
    Seven industries are proposed with specific ranges, which are subject to change, in particular Ship Building's one:

    Industry Fillets' range Chamfers' range
    Power Train 0mm - 15mm 0mm-15mm
    BiW (Body in White) 1mm - 100mm 1mm-100mm
    Consumer Goods 0mm - 50mm 0mm-50mm
    Ship Building 0mm - infinity 0mm-infinity
    High Tech 0mm - 1.5mm 0mm-1.5mm
    Building 1mm - 100mm 1mm-100mm
    Machine Design 0mm - 15mm 0.03mm-1.5mm; angles range: 30deg-60deg

    Below you will find an example of Fillets illustrating the influence of Recognition context setting.

    Propagation type: Depression

         
    The horizontal face is selected as element to extract. Recognition context: BiW
    As the fillets' radius belongs to BiW's radii range, the top vertical face is added to the selection, along with the three fillets connected to the two faces.    		 Recognition context: High Tech
    As the fillets' radius does not belong to High Tech's radii range, the selection is propagated to all faces connected to the selection by fillets, and it stops when reaching a sharp edge between faces that form no depression.

    Propagation type: Protrusion

       
    The horizontal face is selected as element to extract. Recognition context: BiW
    The whole 'seat' is added to the selection. As the fillets' radius belongs to BiW's radii range, it is checked if the 'seat's' faces form a protrusion with the pedestal's top face. As this is not the case, the propagation stops (but includes the fillet).    		 Recognition context: High Tech
    As the fillets' radius does not belong to High Tech's radii range, the selection is propagated to all faces connected to the selection by fillets, including the pedestal's top face. As the pedestal's top face form a protrusion with the pedestal's other faces, they are added to the selection.

    Below you will find an example of Chamfers illustrating the influence of Recognition context setting.

    Propagation type: Depression

         
    The horizontal face is selected as element to extract. Recognition context: BiW
    As the chamfers' length belongs to BiW's chamfers range, the top vertical face is added to the selection, along with the three chamfers connected to the two faces.    		 Recognition context: High Tech
    As the chamfers' length does not belong to High Tech's chamfers range, the selection is propagated to all faces that form a depression with the selection and it stops when the neighboring face forms no depression with the selection (and it does not include the neighboring face that forms no depression with the selection).

     

    Propagation type: Protrusion

         
    The horizontal face is selected as element to extract. Recognition context: BiW
    The whole 'seat' is added to the selection. As the chamfers' length belongs to BiW's chamfers range, it is checked if the 'seat's' faces form a protrusion with the pedestal's top face. As this is not the case, the propagation stops (but includes the chamfer).    		 Recognition context: High Tech
    As the chamfers' length does not belong to High Tech's chamfers range, the selection is propagated to all faces that form a protrusion with the selection and it stops when the neighboring face forms no protrusion with the selection (and it does not include the neighboring face that forms no protrusion with the selection).

  5. Click Show parameters>> to display further options. They are only valid for curves.

    These options are only valid for curves.
     
    • Distance Threshold: specifies the distance value between 0.001mm and 0.1 mm below which the elements are to be extracted.
      • The default value is 0.1mm, except if a Merging Distance has been defined different from 0.001mm in Tools > Options. In this case,
        the Distance Threshold value is initialized with the Merging Distance value.
        To have further information, refer to the General Settings chapter.
       
      • It is available with all propagation types, except for the No propagation type.
    • Angular Threshold: specify the angle value between 0.5 degree and 5 degree below which the elements are to be extracted (the default
      value is 0.5deg)
    • Curvature Threshold: specifies a ratio between 0 and 1 which is defined as follows:

      if ||Rho1-Rho2|| / max (||Rho2||,||Rho1||) < (1-r)/r 
      where Rho1 is the curvature vector on one side of the discontinuity, Rho2 the curvature vector on the other side, and r the ratio specified
      by the user;
      then the discontinuity is smoothed. 

      For example, r=1 corresponds to a continuous curvature and r=0.98 to the model tolerance (default value). A great discontinuity will
      require a low r to be taken into account.
     
      Curvature Threshold = 0.98 Curvature Threshold = 0.80 Curvature Threshold = 0.50
    To sum up:
    • when Point continuity is selected, only the Distance Threshold is activated
    • when Tangent continuity is selected, both Distance and Angular Thresholds are activated
    • when Curvature continuity is selected, all Thresholds are activated.

  6. Click OK to extract the element.

    The extracted element (identified as Extract.xxx) is added to the specification tree.
 

Additional Parameters
 
  • Selecting Complementary mode check box highlights and therefore selects the elements that were not previously selected, while deselecting the elements that were explicitly selected.
  • Selecting Federation check box generates groups of elements belonging to the resulting extracted element that will be detected together with the pointer when selecting one of its sub-elements. For further information, see Using the Federation Capability.

  • You can select a volume as the element to be extracted.
    To do so, you can either:

    • select the volume in the specification tree, or

    • use the User Selection Filter toolbar and select the Volume Filter mode.
      For further information, refer to the Selecting Using A Filter chapter in the CATIA Infrastructure User's Guide.

      In both cases, the result of the extraction is the same whatever the chosen propagation type.
  • If you extract an internal edge, you are advised to select a support element so that the orientation of the resulting extract feature remains the same even if the geometry is modified.
    If you extract an internal edge using the Point Propagation type and there is an ambiguity about the propagation side, a warning message is issued and you are prompted to select a support surface. In this case, the Support field becomes active.
  • Select the Create one extract per propagated cell check box to create one extract feature per propagated cell.
 

Creating Contextual Extracts
  Some commands allow the creation of contextual extracts using the right-mouse button. They are aggregated to the feature using them and put in no show.
 
  • If you select the Create Extract contextual command, the Extract Definition dialog box opens.
 
  • If you select the Create Extract (in point) or Create Extract (in tangency) contextual command, no dialog box opens.
    Both commands let you create extracts with a pre-defined propagation. You just need to select a sub-element such as wire edge, border edges, face, sub-elements of a volume or a solid.
    You cannot select edges as a support is needed.
    You need to leave the mouse on the pre-selected sub-element to preview and compute the propagation (in green):
     
 

Editing Extracts
  When editing extracts, the multi-selection capability is not available: if you select another element to be extracted, it is not appended to the list but replaces the former element.
 

Miscellaneous
 
  • In a .CATProduct document containing several parts, you can use the extract capability in the current part from the selection of an element in another part, provided the propagation type is set to No Propagation.
    In this case, a curve (respectively a surface or point) is created in the current part if the selected element is a curve (respectively a surface or point); the Extract parent therefore being the created curve (respectively the surface or point).
    Note:
    • if another propagation type is selected, the extraction is impossible and an error message is issued.
    • when editing the extract, you can change the propagation type providing the parent belongs to the current part.
    • in the current part, if you select an element using the Tangent, Point or Curvature continuity as the propagation type, a warning is issued and you have to select No propagation instead.
  • If the selected element is not tangent continuous and the propagation type is set to Tangent continuity, an error message is issued.
  • If the selected element is a wire that is not curvature continuous and the propagation type is set to Curvature continuity, an error message is issued.
  • If the selected element has a support face and is not a surface, even though the Complementary mode option is checked, the Complementary mode will not be taken into account for the extraction and the option will therefore be inactive. After the extraction, the option will be available again.
  • If the selected element is a border edge, the propagation is done along the boundary of the support and does not take into account internal edges.
  • When the result of an extract is not connex (during creation or edition) due to naming ambiguity, you can then select the part to keep to solve the ambiguity.
  • If two elements have a same name and their centers of gravity are at a distance of less than 0.1mm, the naming ambiguity mechanism fails and an error message is issued.
  • You cannot copy/paste an extracted element from a document to another. If you wish to do so, you need to copy/paste the initial element first into the second document then perform the extraction.
  • If there is several solutions for the propagation, the computation of the extract stops at the junction point.