POV-Ray : Newsgroups : povray.bugreports : sphere slicing problem Server Time
1 Dec 2021 17:31:21 EST (-0500)
  sphere slicing problem (Message 31 to 37 of 37)  
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From: jr
Subject: Re: sphere slicing problem
Date: 3 Nov 2019 13:35:01
Message: <web.5dbf1cf7401c5809feeb22ff0@news.povray.org>
hi,

William F Pokorny <ano### [at] anonymousorg> wrote:
> On 11/3/19 8:56 AM, jr wrote:
> > William F Pokorny <ano### [at] anonymousorg> wrote:
> ...
> > open to ideas.  more function voodoo, I bet.  :-)
>
> :-) Ah sorry, I aimed my response toward doing as much in POV-Ray as
> possible given you seemed averse to intersecting the shapes with solid
> pigments and using a stand-alone edge detection program.

yes, SDL as much as possible/feasible.  not so much "averse" as .. ignorant of,
ie I have not had cause to use such s/wares before.  if you know of a suitable
utility which will process a set of images like the ones I'm likely to
encounter, please recommend.

> To just try the -render perspective camera above, below and combine
> idea- do one set of frames with the camera above and stick those frames
> in a directory aboveFramesDir and similarly a camera below scan.
>
> You're already using your own image->df3 program. Read in both above
> frame and below frame images and take the max r,g,b found before you
> write the df3 sample position. If the method works, refinements in
> position etc, can wait until you find you need them. Might be the basic
> idea doesn't work for some reason I don't see(1)...

yes, 'df3util' can import PNG, either as grayscale or _one_ of RGBA, so I don't
see/use colours at that stage.  :-(  still, I'd like to understand better the
way you outlined in the previous post, ie using a third cam to post-process the
two perspective cams slices (iiuc).

> (1) - There are issues where any scan approach will run into
> complications beyond those being considered presently. Interior textures
> different than outside textures for objects scanned, for example.

another can of worms.  </sigh>  ;-)


regards, jr.


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From: William F Pokorny
Subject: Re: sphere slicing problem
Date: 4 Nov 2019 08:23:31
Message: <5dc02653$1@news.povray.org>
On 11/3/19 1:31 PM, jr wrote:
> hi,
> 
> William F Pokorny <ano### [at] anonymousorg> wrote:
> 
> yes, 'df3util' can import PNG, either as grayscale or _one_ of RGBA, so I don't
> see/use colours at that stage.  :-(  still, I'd like to understand better the
> way you outlined in the previous post, ie using a third cam to post-process the
> two perspective cams slices (iiuc).
> 
...

What I had in mind was to create two pigments which are planar image 
maps of say sliceDown00.png and sliceUp00.png, respectively. Call these 
PigDown and PigUp. (You might need to rotate/scale to align with the 
final orthographic camera - max_extent() can grab the input image x,y 
size)

Wrap these two pigments in functions (only way they'll get used):

#declare FnDown = function { pigment { PigDown } }
#declare FnUp = function { pigment { PigUp } }

Use these in the use_defined the PigmentMaxUpDownPerspective I mentioned 
previously and use that texture with ambient 1 or emission 1 (diffuse 0 
use no lights) to texture a plane. Place this plane in front of an 
orthographic camera and render to get your real sample taking the max 
r,g,b values for each pixel from the down, up slices. This third render 
is your slice00 sample. Here we are using POV-Ray as an image processing 
tool. Something at which it's very good - if not as fast as dedicated 
image processing tools.

FYI. There might be typos in my SDL, I didn't set up a small scene as I 
often do.

Bill P.


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From: Bald Eagle
Subject: Re: sphere slicing problem
Date: 4 Nov 2019 14:15:00
Message: <web.5dc0778e401c58094eec112d0@news.povray.org>
So, just thinking out loud about this a little more,

If much of the issues arise from the angle between the camera and the surface,
I'm wondering what sort of improvement there would be if the scene were done
with an orthographic camera, but set off to the side by some angle.

Then you'd get an oblique view of the slice, and the ray-object intersection
that the solver would have to deal with wouldn't hit the same issues.

Then you take that render and scale it to stretch it back out and faux-undo the
angled view.  Perhaps if it only required a few degrees offset, it might not
introduce significant distortion.


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From: jr
Subject: Re: sphere slicing problem
Date: 4 Nov 2019 14:50:11
Message: <web.5dc07ff0401c5809feeb22ff0@news.povray.org>
hi,

William F Pokorny <ano### [at] anonymousorg> wrote:
> On 11/3/19 1:31 PM, jr wrote:
> > yes, 'df3util' can import PNG, either as grayscale or _one_ of RGBA, so I don't
> > see/use colours at that stage.  :-(  still, I'd like to understand better the
> > way you outlined in the previous post, ie using a third cam to post-process the
> > two perspective cams slices (iiuc).
> ...
> What I had in mind was to create two pigments which are planar image
> maps of say sliceDown00.png and sliceUp00.png, respectively. Call these
> PigDown and PigUp. (You might need to rotate/scale to align with the
> final orthographic camera - max_extent() can grab the input image x,y
> size)
>
> Wrap these two pigments in functions (only way they'll get used):
>
> #declare FnDown = function { pigment { PigDown } }
> #declare FnUp = function { pigment { PigUp } }
>
> Use these in the use_defined the PigmentMaxUpDownPerspective I mentioned
> previously and use that texture with ambient 1 or emission 1 (diffuse 0
> use no lights) to texture a plane. Place this plane in front of an
> orthographic camera and render to get your real sample taking the max
> r,g,b values for each pixel from the down, up slices. This third render
> is your slice00 sample.

a fair amount of work + organising but (gut feeling) up + down combined ought to
catch 100% of the info.  (perhaps even at slightly less insane quality settings
than used now. :-))  I need to work out real detail[*] but think two template
scenes and three ini files should cover it.

[*] pen + paper.  :-)

> Here we are using POV-Ray as an image processing
> tool. Something at which it's very good - if not as fast as dedicated
> image processing tools.

lack of speed is a drawback during development, but hey..

> FYI. There might be typos in my SDL, I didn't set up a small scene as I
> often do.

I'm glad you're giving such detailed advice + feedback, and will probably need
more in a few days time.  :-)  thanks.


regards ,jr.


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From: jr
Subject: Re: sphere slicing problem
Date: 4 Nov 2019 14:50:12
Message: <web.5dc0808b401c5809feeb22ff0@news.povray.org>
hi,

"Bald Eagle" <cre### [at] netscapenet> wrote:
> So, just thinking out loud about this a little more,
>
> If much of the issues arise from the angle between the camera and the surface,
> I'm wondering what sort of improvement there would be if the scene were done
> with an orthographic camera, but set off to the side by some angle.

won't work unfortunately.  either object is in view, or not.

> ...


regards, jr.


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From: jr
Subject: Re: sphere slicing problem
Date: 6 Nov 2019 12:05:01
Message: <web.5dc2fd24401c5809feeb22ff0@news.povray.org>
"jr" <cre### [at] gmailcom> wrote:
> William F Pokorny <ano### [at] anonymousorg> wrote:
> > ...
> > What I had in mind was to create two pigments which are planar image
> > maps of say sliceDown00.png and sliceUp00.png, respectively. Call these
> > PigDown and PigUp. (You might need to rotate/scale to align with the
> > final orthographic camera - max_extent() can grab the input image x,y
> > size)
> >
> > Wrap these two pigments in functions (only way they'll get used):
> >
> > #declare FnDown = function { pigment { PigDown } }
> > #declare FnUp = function { pigment { PigUp } }

ok, a first basic test confirms the approach works.  thanks.  it seems that in
the combined pigment, the lines are less smooth than in the two source images.
need to explore this over the coming days.  did I say "thank you"?  :-)


regards, jr.


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From: jr
Subject: Re: sphere slicing problem
Date: 8 Nov 2019 20:50:01
Message: <web.5dc61a2d401c5809feeb22ff0@news.povray.org>
"jr" <cre### [at] gmailcom> wrote:
> "jr" <cre### [at] gmailcom> wrote:
> > William F Pokorny <ano### [at] anonymousorg> wrote:
> > > ...
> > > What I had in mind was to create two pigments ...
>
> ok, a first basic test confirms the approach works.  ...

that test was done with two images, names hardwired.  while listening to BBC
Radio 6 Music celebrating an 'Chemical Brothers' album, I managed to get ..
stuff done.  :-)  cannot be bothered to render a full rotation of the resulting
DF3s, so have posted a VMRL version[*].  next (in the coming days) I'll see how
it goes with a couple of complex shapes.  happy days..

[*] in p.b.misc again.


regards, jr.


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