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So, I was trying out creating a part using an edited blueprint image, and I
needed to use the water_level keyword to remove that bit of base plane.
Then I nearly lost my mind trying to figure out why things "weren't working"
when I tried to difference out a cylinder for nice clean hole - and the cylinder
was VISIBLE - but only on one side... :O
Well, apparently the water_level "deleted" section doesn't get deleted - it just
isn't visible.   But when the cylinder gets differenced from it, that surface
becomes visible, even if the cylinder doesn't have a texture, and the whole CSG
gets an overall texture.
That complicates things more than you'd think, because I do a lot of scaling in
the heightfield definition, and now I have to do that in a separate CSG
operation to difference away a box, or intersect one, etc.
What do we think?   Is this a "bug"?
Has anyone ever seen this before?
 
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Attachments: 
Download 'hf part w difference.png' (422 KB)
 
  
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From: Thomas de Groot 
Subject: Re: Unintended behaviour of heightfield in CSG difference? 
Date:  9 Oct 2019 02:46:18 
Message: <5d9d823a$1@news.povray.org> 
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Op 09/10/2019 om 02:53 schreef Bald Eagle:
> 
> 
> What do we think?   Is this a "bug"?
> Has anyone ever seen this before?
> 
I seem to hear a bell tolling in the far distance, muffled by thick mist 
banks... ;-)
Maybe it is best not to use water_level in this particular case and do a 
CSG difference, intersection, or clipping instead. Have you tried that? 
and what is the result?
-- 
Thomas
 
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From: Alain Martel 
Subject: Re: Unintended behaviour of heightfield in CSG difference? 
Date:  9 Oct 2019 11:17:26 
Message: <5d9dfa06@news.povray.org> 
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> 
> So, I was trying out creating a part using an edited blueprint image, and I
> needed to use the water_level keyword to remove that bit of base plane.
> 
> Then I nearly lost my mind trying to figure out why things "weren't working"
> when I tried to difference out a cylinder for nice clean hole - and the cylinder
> was VISIBLE - but only on one side... :O
> 
> Well, apparently the water_level "deleted" section doesn't get deleted - it just
> isn't visible.   But when the cylinder gets differenced from it, that surface
> becomes visible, even if the cylinder doesn't have a texture, and the whole CSG
> gets an overall texture.
> 
> That complicates things more than you'd think, because I do a lot of scaling in
> the heightfield definition, and now I have to do that in a separate CSG
> operation to difference away a box, or intersect one, etc.
> 
> 
> What do we think?   Is this a "bug"?
> Has anyone ever seen this before?
> 
Instead of water_level, use an intersection with a box. That way, your 
height_field will get a true back side and behave correctly when you 
perform some other CSG operations.
 
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