CAD software discussion forum > 3D CAD/CAM > How does Concatenate edges work?

How does Concatenate edges work?

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Registered: 2011-9-17

Message 1 of 2

 How does Concatenate edges work?
25-09-2008 07:25 . pm | View his/her posts only
Hi Mike,

I know what concatenate edges should do and why I'd like to do it more often.

BUT, I can not find any way of using it. I am presuming two adjacent surfaces can be sewn then have the two adjcent edges concatenated so an extrusion of this edge would result in a single face.

I just cannot get a concatenate to stick. Someone care to explain all the in's and outs??? Perhaps a SnT .....


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posts: 2

Registered: 2011-11-22

Message 2 of 2

26-09-2008 05:46 . am | View his/her posts only
Hello mudcrab

The actions you are describing are initially sew, not concatenate, so for everyone else the distinction needs to be explained.

You sew face/surface edges together so that they share the same edge boundary. In this process, the program is extending-trimming them so that they meet accurately. Actually, without wishing to confuse, each face continues to have it's own edges, the two faces together make a Shape, so they are sharing a Shape edge boundary. The reason the term "boundary" is used is because it could actually be made of more than one element - when you hover your mouse along what seems to be one continuous edge (with the filter set to "edge"), you may well find that one edge is in fact many. When the faces do share the same Shape edge, the display of the edge is shown in solid line font instead of small-dash (when viewing in wireframe mode). Another interesting fact on how VX surface/face technology works - if you have a face that is on it's own, not connected to anything else, it is counted as an Open Shape. I have seen people spend a lot of time inverting faces so that the are the correct way round, because the system displays them "inside out". However, what VX is doing is constantly testing for a closed volume (closed Shape). Once you have a water-tight model, VX will ensure that all the faces are correctly orientated (even with imported geometry).

So, back to concatenation. The wireframe tool cannot concatenate face edges, but you can extract edges and then concat those into a single complex wireframe curve from the edge data - useful for extrude etc. See the Wireframe Tab, 8th button from the right, 1st pop-down button, "curve from edge" and concatenate curves is the 7th button from the left, 1st pop-down button. These commands can be used to collect continuous edge data from a face and that face does not have to be sewn to any adjacent face first.

If you actually want to "concatenate" the elements of a face edge, there is a separate tool for this as well - "concatenate edges". This is a good tool for fixing "faceted" edges that you have been presented with via imported geometry - there are some CAD systems out there that always produce fragmented edges (boo!). The command is found on the FreeForm Tab, 10th button from the left, 5th pop-down button. It removes the 0.000 "gaps" between the elements such that the edge becomes one continuous entity. The tool can be tweaked with a tolerance for allowable angle, the default 5degrees should be fine in most circumstances. If that edge is to be sewn to another, then the other will need to be modified too if it is not already single continuous element. If the concat was a success, an operation for it is added to the history tree.
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