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Old 16th June 2006, 06:30 PM   #1
Stiglr
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Default Convex Hull problems

Why is it that sometimes, when I try to create a convex hull from a pair of cross sections, the software often just 'decides' which vertices to ignore completely in making a new shape?

For example, say I'm modeling a vertical stabilizer and rudder. I make a poly shape of the filet of the piece and another of the profile of the piece and arrange them perpendicular to each other in the proper place to describe the entire tail unit. Now let's say the trailing edge of the rudder has a nice curved edge leading towards where it will join the fuselage...

I create the polys of both shapes, select all the vertices, and do a Convex Hull. The result I get is a straight line between the trailing edge, and the polys I'd set to describe the scalloped edge just aren't there anymore. The rest of the shape is exactly what I had in mind.

What's the trick to getting this feature to obey instructions?
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Old 17th June 2006, 02:08 AM   #2
Andy
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Default Re: Convex Hull problems

The key word is 'convex'. If you imagine shrinking a rubber balloon over the vertices, any vertices which are not 'on the edge' will not touch the balloon. For a vertex to be part of the final shape, it must 'stick out'. If there's a vertex you need to have in the final shape, move it outwards, do the convex hull, and then move the vertex back.

It's more like putting a (deflated) balloon around the vertices, rather than 'vacuum packing'.

Last edited by Andy; 17th June 2006 at 03:29 AM.
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Old 17th June 2006, 08:13 PM   #3
Stiglr
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Default Re: Convex Hull problems

I'll try that, thanks!!!
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Old 19th June 2006, 01:22 PM   #4
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Default Re: Convex Hull problems

This is the point at which I do a manual hull...
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Old 26th June 2006, 09:12 PM   #5
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Default Re: Convex Hull problems

hmmmm. I never really thought of doing a convex shape hull design. ooh interest. I think I will do a convex hull design in my next project.
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