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Old 8th March 2023, 02:18 AM   #1
DaveS
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Default Preventing visible edges after boolean operation

Hey.

So I am working on a 3D model of the Hubble Space Telescope (HST) and I have a problem with visible edges for the cut-outs in the Aft Shroud section for the two of the three Fixed Head Star Trackers. I have attached a screenshot of this. They were created by using a boolean subtraction operation on the main AS bay doors that they are part of.

Any ideas on how to get rid of these visible ugly edges?
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Old 9th March 2023, 07:44 AM   #2
Andy
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Default Re: Preventing visible edges after boolean operation

There are a couple of quick techniques I use to find these problems. Firstly, set all surfaces to single-sided (1S on control panel). If any become non-visible, they may need their normals flipping. Secondly, temporarily increase the subdivision. This can allow you to spot holes and problems with the geometry.


You may be able to Object->Optimize-vertices/surfaces out the problems but you may also need to use the Edit->Select-vertices/surfaces menus to select problematic geometry and then remove it.
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Old 9th March 2023, 09:04 AM   #3
DaveS
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Default Re: Preventing visible edges after boolean operation

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Originally Posted by Andy View Post
There are a couple of quick techniques I use to find these problems. Firstly, set all surfaces to single-sided (1S on control panel). If any become non-visible, they may need their normals flipping. Secondly, temporarily increase the subdivision. This can allow you to spot holes and problems with the geometry.


You may be able to Object->Optimize-vertices/surfaces out the problems but you may also need to use the Edit->Select-vertices/surfaces menus to select problematic geometry and then remove it.
Tried all that. This is a simple cylinder with a diameter of 4.258 m and a height of 3.495 m. The FHST cut-outs are roughly the shape of an ellipse with a wider base as seen on the schematic attached to this post.
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Old 9th March 2023, 09:20 AM   #4
Andy
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Default Re: Preventing visible edges after boolean operation

Send me the file and I'll take a look,
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Old 9th March 2023, 11:23 AM   #5
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Default Re: Preventing visible edges after boolean operation

It's because everything is broken into triangles. If you triangulate the final model, you'll see how it is ultimately rendered, where one surface can be broken into many triangles. Of course you could model in flat-shaded geometry, which would hide any of the slight plane/float-rounding variations. But that's probably not what you want.

The best thing to do is to minimize the larger surfaces areas before you do a boolean.

In this case, I used a couple of boxes as a knife-booleans to chop up the surfaces into rectangles, before doing the final cut-boolean. That reduces the surfaces area of the triangles.
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Old 9th March 2023, 01:09 PM   #6
DaveS
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Default Re: Preventing visible edges after boolean operation

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Originally Posted by Andy View Post
It's because everything is broken into triangles. If you triangulate the final model, you'll see how it is ultimately rendered, where one surface can be broken into many triangles. Of course you could model in flat-shaded geometry, which would hide any of the slight plane/float-rounding variations. But that's probably not what you want.

The best thing to do is to minimize the larger surfaces areas before you do a boolean.

In this case, I used a couple of boxes as a knife-booleans to chop up the surfaces into rectangles, before doing the final cut-boolean. That reduces the surfaces area of the triangles.
Thanks, the trick using the boxes and minimizing the surface area worked a treat! Got the FHST openings done nicely and things look good now.
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