I received a few questions about an earlier article with regards to getting expected results from direct geometry edits. When you start pulling on various faces of your model you may or may not get what you are expecting. This applies to both history-free direct edits as well as history-based direct edits. To show this in its simplest form I will use the simple model shown below. In this case we are pulling on the yellow face.
With a linear pull there are at least four different possible solutions to this edit.
- #1 - The pull face changes size as the adjacent faces are stretched
- #2 - The pull face size is maintained, the adjacent faces are stretched and the angle of the top face is changed, topology is unchanged
- #3 - The pull face size is maintained, the angle of the top face is unchanged and topology is changed – a new face is created
- #4 - The pull face changes from a planar face to a b-spline surface
There are certainly other possible results if you pull around an axis.
With history-free modeling there may not be any relationships or conditions built into the model that would drive any one particular result. As such the results are completely based on the type of command or command options that may be available to the user.
For direct edits in a history-based system, the result may be completely dependent on how the model was originally created, as with any other edit in a history-based system.
In the history-free category, with their instantaneous graphical feedback, SpaceClaim certainly leads the way in helping the user understand the results immediately. I just personally struggle in SpaceClaim finding the right options to get different results, but I’m no expert with SpaceClaim.
Siemens is following SpaceClaim with the instant feedback, but again getting different results seems difficult for me. #1 and #3 are easy to get with the Pull Face or Move Face commands. The others???
CoCreate Modeling provides all the options for getting any of the results above, but it does not yet have the instant graphical feedback for case #1 and #2, although I am sure this is quickly changing.
As with any CAD tool, it takes some practice to understand what is possible and how it’s going to work, but don’t assume that just because it is or is not possible in one system, that it will work the same in others. There's a lot of progress being made in direct editing technology. The nice thing about history-free direct edits is that the results are completely independent of the how the model was originally created. You decide, right at the time of the edit, what results you need and “make it so”.