Extracting Multiple Elements

This task shows how to extract sub-elements (curves, points, surfaces, solids, volumes and so forth) that are joined into one element.

Open the MultipleExtract1.CATPart document.


  1. Click Multiple Extract .

    The Multiple Extract Definition dialog box is displayed.
  2. Select the elements to be extracted.

    If the first selected element is a curve (or a point, a surface, a volume), the next selected element is necessarily a curve (or a point, a surface, a volume).
  3. Choose the Propagation type: 

    If the Intersection edges activation / C1 Intersection edges activation icon is selected in the User Selection Filter toolbar, then the Geometrical Element Filter icon is automatically selected. When you click OK in the Multiple Extract Definition dialog box, the status of the icon returns to normal.
  4. Click Show parameters>> to display further options.

    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 degrees 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.
    If several elements are selected, when you click an element in the list, only the authorized thresholds are enabled according to the propagation type.
  5. Click OK to extract the elements.

    Only one feature (identified as Multiple Extract.xxx) is added to the specification tree.

Additional Parameters

  • Check Complementary mode to highlight and therefore select the elements that were not previously selected, while deselecting the elements that were explicitly selected.
    This option is disabled if the extracted element is a point or a volume.
  • Check Federation to generate 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.
  • If you extract an internal edge that you want to propagate, and there is an ambiguity about the propagation side, a warning message is issued and you are prompted to select a support face. In this case, the dialog box dynamically updates and the Support field is automatically filled in.


  • Providing several elements are selected and can be joined into one element after the propagation (if needed), the propagation is automatically done within the Multiple Extract command. Otherwise, the result is not connex, you are prompted to solve the ambiguity and keep only one sub-element or all the sub-elements. Refer to Managing Multi-Result Operations for further information.
  • In a .CATProduct document containing several parts, you can use the multiple 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).
    • 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), you can select the part to keep to solve the ambiguity.
  • If two elements have the same name and 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.

In case you are using the old multiple edge extract command:

Open the MultipleEdgeExtract1.CATPart document.
  1. Double-click the extracted element.

A warning message is issued...

... as well as the Sketch Extract dialog box:

Only Cancel is available, all other fields and options are grayed out.