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Old 28th August 2009, 04:50 AM   #1
coldby
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Default controlling the extrusion centre

One more, as long as the work leaves me a few inches of loose chain

Extrude Along Path is one of the most powerful tools of AC3D, as it allows you to create any kind of complex objects out of a mere profile.
Yet it has a dark spot that makes it somewhat less versatile than one might wish : there seems to be no way to control the 'extrusion centre', i.e. the point on the "extrudend" that will follow exactly the guiding path.
Let me try to be more specific : as you extrude a surface (or its perimeter) along a path, in the resulting objects its points will become lines. Of these lines only one (or a set of parallel ones) will match exactly the original path, whereas the others will be smaller or larger according to the shape of the extruded surface.

I assume the extrusion centre above is the centre of the surface bonding box, as a few frustrating tests showed it's neither the gravity centre nor the pivot centre.

Controlling the position of this point is little relevant as long as the path is smooth and decently larger than the surface to be extruded (as in fig 1), but when the two are nearly the same size or if the path has comparatively sharp corners (as in fig 2), it may get damn important.

Does anyone know of a way around it?
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Old 1st September 2009, 02:31 PM   #2
thierry_st_malo
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Default Re: controlling the extrusion centre

I quite agree with you, Coldby. I have the very same problem.
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Old 1st September 2009, 05:51 PM   #3
Dennis
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Default Re: controlling the extrusion centre

I agree, it would be nice to be able to specify the object center for this operation.

Meanwhile, there might be a workaround for some cases --- I did a similar test to coldby's and added a "stem" to the "semi-rectangle" object (see attached image). This pushed the object center "up", and gave me some unwanted geometry where the "stem" was (selected). Just a matter of deleting that unwanted geometry at that point.

This can be a situational workaround, however, and I can think many cases where it is not practical --- if AC3D were to use the profile object's center (or perhaps make it configurable to use object center or geometric center), that seems like it'd be a better approach.
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Old 2nd September 2009, 04:04 AM   #4
coldby
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Default Re: controlling the extrusion centre

Hi Dennis! Nice to learn you're still around with both hands in 3D (quite shameful of mine, actually, as I was the one who disappeared )

Yes, I came myself to that workaround and it actually does its job well enough in a number of cases.
Still, as you say, sometimes getting rid of the resulting stray surfaces is a mess, and placing your selected center-point exactly where you wish is even worse.
The latter would be welcome more often than one may think, as in many cases it would be convenient to extrude two objects separately along the same path, and then to merge them after the necessary adjustments have been made.
You certainly can extrude them together and then split the result, but this requires its share of boring work - you must first build a "sum" object by selecting all points in the right order, making a surface and then reducing it to line, which in some cases can be pretty long, tricky and awkward. Besides, even selecting the right surfaces afterwards in order to split the extruded object isn't always a piece of cake

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