Creating a Matching Constraint 

This task explains how to match two surfaces or curves and modify them in order to get the desired matching transition.
The matching principle consists in deforming one geometrical object in order to improve continuities with another geometrical object.
Note: If in the menu Tools > Options > Infrastructure > Part Infrastructure in the Display tab the option Constraints is activated, the Match constraint is added to the specification tree.
  Connect Checker support: Once a Matching constraint is created, the source and target elements can be interactively analyzed by the Connect Checker without the need to exit and re-enter the command.
You simply activate Connect Checker while the Matching Constraints command is active.
Open the Matching.CATPart document.

  1. Click the Matching icon .
    The 'Matching Constraint' dialog box opens.

In the following example, we are going two match two surfaces.
 

  1. Click on the Source surface near the edge you would like to match.

  2. Click on the Target surface near the edge the Source surface has to snap to.

    An arrow appears. Its origin marks the edge which will be matched.



 
 

  1. Click Apply in the Matching dialog box to match the surfaces.

 
 

  1. Undo the last step and click the arrow. The Target surface will now be snapped to Source surface.
    Source and Target can also be inverted by the option Invert.

 
 

  1. Click OK to match the surfaces.
You can define the following options:
 

Elements

  • Source: Selection of the element to be deformed to fulfill the requested conditions.
  • Target: Selection of the target geometry which will not be changed. You can select two surface edges or curves.
    Datum and Feature point elements are also supported as target elements for G0 continuity.
  • Invert: Swap Source and Target.
  • Limits:
    • Partly: Allows to match the source edge to part of the target edge.
      You can specify the limiting points via the selection fields.
      The snap manipulator allows you to snap the vertex of the source element to a point.
      Tip: For partial matchings, it is recommended to use Minimum Corner Distance in Tools > Options > ICEM Shape Design > General tab.
        In case of partial matching constraints, gaps or overlaps may occur if the source surface corners do not coincide with the target surface corners. With Minimum Corner Distance, a corner distance tolerance is specified.
      If the source surface corner is moved with the manipulator, it automatically snaps to the corresponding target surface corner as soon as its position is within the distance from the target surface corner defined by the tolerance.

Approximated and Exact

For matching constraint of surfaces, two types of algorithm are available which can be used together: the exact algorithm and the approximated algorithm.
If both of them are used, the first one to be performed is the exact one, then the approximated.
For matching constraint of curves, only the exact algorithm can be used.

  • Approximated: The control point distribution in the first control point row of the source element remains unchanged. This may cause larger continuity deviations.
    • Orders of continuity: Specifies the matching transition.
    • Begin and End Edge continuities (G3 in ISD only): Aligns the cross tangents at the edges of the source and the target.
      • Begin and End Edge continuities OFF: All cross tangents will be aligned coplanar only, i. e. there may be an angle between the cross tangents of the source and the target.
      • Begin or End Edge continuities ON: The beginning or end cross tangent of the source will be aligned collinear to the beginning or end cross tangent of the target.
      • Begin and End Edge continuities ON: All cross tangents of the source will be aligned collinear to the cross tangents of the target.
      • Lock Boundaries: You can fix the selected boundaries of the source element. Only the other control points are moved. If both boundaries are fixed, only inner control points are moved.
        Input geometry Lock Boundaries at end of edge Lock Boundaries at start and end of edge
  • Exact: Defines the continuity in case of matching curves.
    In case of matching surfaces, the source element adopts the parametrization from the target element. Depending on the selected continuity, the control point distribution is influenced in the rows 1 (G0) to 4 (G3).

    Exact OFF with G0 continuity Exact ON with G0 continuity
  • Opposite: You can change the continuity values to be kept at the opposite edges either via the context menu at the continuity labels in the work area or by these options in the dialog box. The values are automatically updated in the respective environment.
  • Opposite Continuities:
    • Source Opposite:
      These options are available only if the Diffusion option is selected.

      Defines continuities to be kept at the opposite curve end or surface edge of the source.
      When using Diffusion option, control point/row modifications done to achieve the continuity with the target is propagated to other control points/rows than the ones directly involved by the specified continuity. This may move control points/rows at the opposite end or edge and thus modify the continuity at the opposite end or edge.
      At the opposite source curve end point or surface edge, you can specify a maximum continuity to be kept using either the Max. list in the dialog box or in the work area the context menu available at the continuity labels which appear when Diffusion option is selected.
      G0 continuity is set by default, but you can select any other continuity irrespective of whether the order allows to keep it or not. If the continuity cannot be kept, the maximum possible continuity is applied and displayed under Applied in the dialog box marked by asterisks in the context menu.
      The Free option applies no continuity. This allows the movement of all control points or control point rows, without keeping any continuity, to obtain an optimal control point distribution with Diffusion option. As in this case no continuity is kept at opposite, the continuity with neighboring elements at the opposite end point or edge may be broken.
      • Matching constraints between source and target always have priority over the continuity specified at the opposite in case that both continuities cannot be kept.
      • Create another matching constraint between the opposite end point or edge and the other target to manage the wanted continuity at the opposite with the same priority.

      Also see, Mean Surface Solver option in Tools > Options > Shape > Freestyle, Matching Constraint command options section.
    • Target Opposite:
      These options are only available if the following option are selected:
      • Diffusion
      • Under Both, either Mean or Extension

      These options define continuities to be kept at the opposite curve end or surface edge of the target analogous to the Source Opposite options.

    • Options

    • Inside: Projects the edge of the source surface onto the target surface. On the target surface is displayed a preview of the edge position.
      The direction depends on the Support option.
    • Basic Surfaces: Provides the ability to match a source surface to the underlying basic surface of a target surface which is represented by a face.
    • Diffusion: Modifies the maximum number of rows of control points.

    • Adapt: Adopts the order of the target edge from the source.
    • Display deformation distance: Displays the maximum deviation value and its position between the original surface and the modified surface in the graphic area. The original mesh before the modification is also displayed.



      While using the command you can reset the reference. Right-click the arrow of the variant display and select Reset Delta Reference to reset the reference. The existing position of the surface is set as new reference. The reference mesh and the maximum deformation distance are computed with respect to the new reference.
    • Auto Apply: Applies modifications automatically.
    • No Highlight Representations: Deactivates the highlight on the selected elements to avoid conflicts with the display of other entities such as control points.

    Alignment: Every control point row can be organized according to the following criteria:

    • 3-points Plane: Projection orthogonal of control points on a 3 points plane. For each control point row of the surface to match, a plane is defined from the 1st, the 2nd and the last control point. All points of each row are projected into its plane.
    • Mean Plane: Projection orthogonal of control points on a mean plane. For each control point row of the surface to match a mean plane is defined, and all points of each row are projected into its plane.

    Both: Both input elements are modified, the source and the target.
    Depending on the selected continuity G0 to G3, up to four control points (in case of curves) or control point rows (in case of surfaces) are moved.

    • Mean: In case of matching curves, the endpoints of the input curves to be connected are moved to the midpoint of their connecting line:

      Curve matching with option Both > Mean with G0 continuity


      In case of matching surfaces, the common edge is defined by the midpoints of the connecting lines between the opposite points of the edges to be connected:

      Surface matching with option Both > Mean with G0 continuity

    • Extension: In case of matching curves, the endpoints of the input curves to be connected are moved to the intersection point of the tangential extension of the curves.
      In case of matching surfaces, the resulting common edge is the intersection curve of the tangential extension of the input surfaces:

      Surface matching with option Both > Extension with G0 continuity

    • Common Edge: In case of matching curves, the endpoints of the input curves to be connected are moved to the midpoint of the connecting line between the second control points of both curves, so that G1 continuity is created:

      Curve matching with option Both > Common Edge with G1 continuity



      In case of matching surfaces, the control point rows input surface edges to be connected are moved into the connecting plane of the second control point rows of both surfaces. The common edge is the midline of the connecting plane:

      Surface matching with option Both > Common Edge with G1 continuity

    Support: Defines the direction in which the control points are projected.

    • Along direction:
      OFF: Moves the control points along the local normal of the target element.
      ON: The movement of control points depends on the propagation mode selected. The following modes are available which define the projection direction:
      • Along View: The direction is along the view direction. The control points move along the depth of the viewpoint. To see the control point movement rotate the part.
      • User Line/Plane: The direction is along the selected line or normal to the selected plane.
        The compass option is available only with this mode. Right-click the compass selection field and select the axis or plane. Using the contextual menu you can create the required element. If Compass is ON, you can set this direction by manipulating the compass in 3D.
      • Along Source: Projects the control points for G1/G2 along the normal of the source.
        If Inside mode is selected, the edge of the surface to be modified (the G0 row) is projected orthogonally on the target surface.

    Gap Options (in ISD only): For a matching constraint with a gap, the Both options are not available.

    • Gap:
      OFF: Matches the source element to the target element without gap with the continuity set.
      ON: Creates the matching constraint with a remaining gap between source and target element for which the following conditions can be specified:
      • Extrapolation: Extrapolates the target surface internally and the source surface matched to the common edge calculated from the internal extrapolation with at least G1 continuity.

      • Parallel: Creates the matching constraint as with Extrapolation. In addition, an offset distance to the common edge internally calculated from the extrapolation will be preserved. G1- G3 information is taken from the target element.

      • Offset fix: Creates the matching constraint at a defined offset value. The offset direction can be defined by a line or by compass direction.

      • Offset norm: Projects the offset distance of the matching constraint in normal direction of the target element.

    Modification Ratio: Specifies a ratio for displaying an intermediate result between the original and last applied status. It helps to control the final result with the best possible solution between all the constraints modifying the particular surface.
    Minimum and maximum values in the Deviation section are updated dynamically when moving the slider.
    Once you exit the Matching Constraint command with certain modification ratio, the next update of the constraint ignores the earlier specified ratio.

    Deviation: If selected, displays the Min Values and Max Values according to the orders of continuity after clicking Apply or OK.

    • G0: Distance - absolute.
    • G1:: Angle between the tangents or normals - absolute.
    • G2: Radius error - relative.
    • G3 (in ISD only): Angle (Envelope of curvature hedgehog) - absolute.