Go Back   AC3D Forums > General > AC3D General
Register FAQ Members List Calendar Search Today's Posts Mark Forums Read

Reply
 
Thread Tools Display Modes
Old 16th June 2006, 06:30 PM   #1
Stiglr
Senior Member
Professional user
 
Stiglr's Avatar
 
Join Date: Feb 2004
Location: Portland, OR
Posts: 604
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?
__________________
Flight Sim Project Contributor

My Gaming Rig:
i5 2500K Quad-Core CPU at 3.3GHz
MSI P67A-C43 mobo
4GB of PC12800 DDR3 memory
Windows 7
1GB Galaxy GeForce GTX550 Ti video card GeForce 270.61 drivers (4/2011)
Cougar joystick/throttle combo
CH Pedals
Stiglr is offline   Reply With Quote
Old 17th June 2006, 02:08 AM   #2
Andy
Administrator
Professional user
 
Andy's Avatar
 
Join Date: Jun 2003
Posts: 4,451
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.
Andy is offline   Reply With Quote
Old 17th June 2006, 08:13 PM   #3
Stiglr
Senior Member
Professional user
 
Stiglr's Avatar
 
Join Date: Feb 2004
Location: Portland, OR
Posts: 604
Default Re: Convex Hull problems

I'll try that, thanks!!!
__________________
Flight Sim Project Contributor

My Gaming Rig:
i5 2500K Quad-Core CPU at 3.3GHz
MSI P67A-C43 mobo
4GB of PC12800 DDR3 memory
Windows 7
1GB Galaxy GeForce GTX550 Ti video card GeForce 270.61 drivers (4/2011)
Cougar joystick/throttle combo
CH Pedals
Stiglr is offline   Reply With Quote
Old 19th June 2006, 01:22 PM   #4
captainj2410
Senior Member
Professional user
 
captainj2410's Avatar
 
Join Date: Aug 2005
Location: Captain's Quarters, Deck 1 USS Avenger NX-101468
Posts: 792
Default Re: Convex Hull problems

This is the point at which I do a manual hull...
captainj2410 is offline   Reply With Quote
Old 26th June 2006, 09:12 PM   #5
nightoftheroundtable
Senior Member
Professional user
 
nightoftheroundtable's Avatar
 
Join Date: Mar 2006
Location: elma washington
Posts: 805
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.
nightoftheroundtable is offline   Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off



All times are GMT -4. The time now is 01:13 PM.


AC3D Forum
(C) Inivis Limited 2020