Editing Parts Without History

ViaCAD contains a collection of tools to edit parts without a history tree.    These tools are invaluable for modifying parts where you:

  • Import the file from another CAD system
  • Remove the tree to simplify the file size or regeneration times
  • Modify a part independent of a pre-defined feature (by face)

Check out the video below showing these interesting tools.


Our first implementation of tools to modify faces independent of features was around 1997. ¬†We had source code to the Local Operations technology from Geometric Software Solutions (GSSL). At the time this was a third party component technology on top of ACIS to perform shelling and draft operations. ¬†Later the technology was acquired by Spatial and tightly integrated into the ACIS kernel. ¬†When you hear feature free modeling hype from CAD vendors typically the underlying workhorse is “Local Operations”. ¬†If you are a software geek, click here for the Spatial docs on Local Operations. Interestingly, Local Operations is also the component name within the Parasolid kernel.

One of the things I found interesting about Local Operations was that the core procedures used to support shelling and draft operations provided a means to manipulate faces.   Generically manipulating faces independent of features is no easy feat since not only do you need to address changes in geometry but topology as well.  Using the Local Operations technology, we went ahead and exposed the core face manipulators with user interfaces.

ViaCAD Editing Tools

ViaCAD has a palette of six tools dedicated to editing faces.  From left to right they are:

localOpsDraft Face

Rotates a collection of faces a specified angle about an edge.

Match Face

Changes the orientation of a planar face to match that of a referenced face.    In addition to matching the orientation, the resulting face is in the same plane.

Move Face

Moves a collection of faces by a translation vector.

Offset Face

Moves the face the same perpendicular distance.

Remove Face

Removes a face and fills in the “hole” by extending neighboring faces.

Replace Face

Replaces a user constructed surface with a selected face.

Extend Surface

Although not in the face edit tool palette, Shark adds another Local Operation specific to surfaces called Extend introduced in Shark FX V7.  This tool will extend a surface along an edge.  Check out the movie below.

Implementation Notes

Performing a face edit operation in ViaCAD will add a history operation to the part. ¬†For example with a face translate, you have access to the dx,dy,dz parameters which ¬†you can change at any time through the history tree located in Concept Explorer. ¬†If you do ¬†not want the part to retain history, go to the Edit:Remove Links command. The Remove Links command will remove all history related to the part. History or no history is the designer’s choice within ViaCAD.


Over the years I have become a big fanboy of Local Operations.  But there are some things it still needs to improve upon, in particular working with NURB surfaces. Many  of the demos you see showing off feature free modeling are using analytical surfaces.  Reality sets in with complex NURB based found in  automobile, airplane, or free form consumer products. Part of the reason are the technology limits/assumptions regarding extending NURB based surfaces and the ways these surfaces can be extended.  Hopefully we will see some improvement in this area in upcoming versions from ACIS.

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