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From: Mike Horvath
Subject: Re: Mysterious vanishing isosurface
Date: 11 Dec 2016 04:55:04
Message: <584cdc28$1@news.povray.org>
On 12/8/2016 9:36 PM, Mike Horvath wrote:
> If I rotate the camera 90 degrees around the x axis, the isosurface
> disappears.
>
> Mike

I increased the max_gradient to 10000, and there seems to be no improvement.

Mike


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From: William F Pokorny
Subject: Re: Mysterious vanishing isosurface
Date: 11 Dec 2016 14:09:22
Message: <584d5e12$1@news.povray.org>
On 12/10/2016 07:50 AM, Mike Horvath wrote:
> On 12/9/2016 12:55 PM, William F Pokorny wrote:
>> On 12/08/2016 09:36 PM, Mike Horvath wrote:
>>> If I rotate the camera 90 degrees around the x axis, the isosurface
>>> disappears.
>>>
>>> Mike
>>
>> Is there any chance the camera is ending up inside the contained_by
>> shape for the isosurface?
>>
>> Bill P.
>
> I don't think so. My camera is 17 units away from the origin, and the
> contained_by area is only 1 unit wide.
>
> (These values then get scaled by 200000.)
>
> Mike

OK - it was a shot in the dark. I've not followed your color space 
function() development.

A suggesting is trying the isosurface coded in your scene at a rotations 
around where it is breaking up, at a low resolution, no aa+, area light, 
etc., as

isosurface {
}

not used by reference (github #114 (#113 is related)), so you get some 
idea what the max gradient really is and how it is changing.

Bill P.


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From: clipka
Subject: Re: Mysterious vanishing isosurface
Date: 11 Dec 2016 22:35:55
Message: <584dd4cb$1@news.povray.org>
Am 11.12.2016 um 15:09 schrieb William F Pokorny:

> A suggesting is trying the isosurface coded in your scene at a rotations
> around where it is breaking up, at a low resolution, no aa+, area light,
> etc., as
> 
> isosurface {
> }
> 
> not used by reference (github #114 (#113 is related)), so you get some
> idea what the max gradient really is and how it is changing.

Thanks for bringing this report and analysis up again; I had wondered
recently why my own toying-around with Mike's isosurfaces didn't prompt
any max gradient warnings, but didn't take the time to investigate.

I've just published a new version that supersedes the offending
mechanism with something smarter, and should again report the max
gradient as expected, for each and every isosurface actually rendered,
yet aggregating the results for any clones.

https://github.com/POV-Ray/povray/releases/tag/v3.7.1-alpha.8913469


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From: Mike Horvath
Subject: Re: Mysterious vanishing isosurface
Date: 11 Dec 2016 23:50:58
Message: <584de662$1@news.povray.org>
On 12/11/2016 9:09 AM, William F Pokorny wrote:
> On 12/10/2016 07:50 AM, Mike Horvath wrote:
>> On 12/9/2016 12:55 PM, William F Pokorny wrote:
>>> On 12/08/2016 09:36 PM, Mike Horvath wrote:
>>>> If I rotate the camera 90 degrees around the x axis, the isosurface
>>>> disappears.
>>>>
>>>> Mike
>>>
>>> Is there any chance the camera is ending up inside the contained_by
>>> shape for the isosurface?
>>>
>>> Bill P.
>>
>> I don't think so. My camera is 17 units away from the origin, and the
>> contained_by area is only 1 unit wide.
>>
>> (These values then get scaled by 200000.)
>>
>> Mike
>
> OK - it was a shot in the dark. I've not followed your color space
> function() development.
>
> A suggesting is trying the isosurface coded in your scene at a rotations
> around where it is breaking up, at a low resolution, no aa+, area light,
> etc., as
>
> isosurface {
> }
>
> not used by reference (github #114 (#113 is related)), so you get some
> idea what the max gradient really is and how it is changing.
>
> Bill P.

I don't understand. What are you saying?

Mike


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From: clipka
Subject: Re: Mysterious vanishing isosurface
Date: 12 Dec 2016 00:08:22
Message: <584dea76$1@news.povray.org>
Am 12.12.2016 um 00:51 schrieb Mike Horvath:

>> A suggesting is trying the isosurface coded in your scene at a rotations
>> around where it is breaking up, at a low resolution, no aa+, area light,
>> etc., as
>>
>> isosurface {
>> }
>>
>> not used by reference (github #114 (#113 is related)), so you get some
>> idea what the max gradient really is and how it is changing.
>>
>> Bill P.
> 
> I don't understand. What are you saying?

He's suggesting that rather than

    #declare Whatever = isosurface {...}
    ...
    object { Whatever }

you should use (at least temporarily)

    isosurface {...}

as this will allow POV-Ray to give you a warning if it thinks your
max_gradient is a poor choice (whether unnecessarily high or too low).


Alternatively, use the brand-new development release I posted about a
couple of minutes ago, which should be able to do the same stunt without
any changes to your scene file.


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From: Mike Horvath
Subject: Re: Mysterious vanishing isosurface
Date: 12 Dec 2016 02:11:22
Message: <584e074a$1@news.povray.org>
On 12/11/2016 7:08 PM, clipka wrote:
> Am 12.12.2016 um 00:51 schrieb Mike Horvath:
>
>>> A suggesting is trying the isosurface coded in your scene at a rotations
>>> around where it is breaking up, at a low resolution, no aa+, area light,
>>> etc., as
>>>
>>> isosurface {
>>> }
>>>
>>> not used by reference (github #114 (#113 is related)), so you get some
>>> idea what the max gradient really is and how it is changing.
>>>
>>> Bill P.
>>
>> I don't understand. What are you saying?
>
> He's suggesting that rather than
>
>     #declare Whatever = isosurface {...}
>     ...
>     object { Whatever }
>
> you should use (at least temporarily)
>
>     isosurface {...}
>
> as this will allow POV-Ray to give you a warning if it thinks your
> max_gradient is a poor choice (whether unnecessarily high or too low).
>
>
> Alternatively, use the brand-new development release I posted about a
> couple of minutes ago, which should be able to do the same stunt without
> any changes to your scene file.
>


"Shutdown Warning: The maximum gradient found was 32.504, but 
max_gradient of the isosurface was set to 100.000. Adjust max_gradient 
to get a faster rendering of the isosurface."

According to this, max_gradient setting is not the problem, right?

Mike


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From: Mike Horvath
Subject: Re: Mysterious vanishing isosurface
Date: 12 Dec 2016 03:09:38
Message: <584e14f2$1@news.povray.org>
On 12/8/2016 9:36 PM, Mike Horvath wrote:
> If I rotate the camera 90 degrees around the x axis, the isosurface
> disappears.
>
> Mike

I'm not sure why, but increasing the contained_by box fixed the problem. 
I used:

	contained_by
	{
		box {-1,1}
	}

instead of:

	contained_by
	{
		box {0,1}
	}


Mike


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From: clipka
Subject: Re: Mysterious vanishing isosurface
Date: 12 Dec 2016 03:23:48
Message: <584e1844@news.povray.org>
Am 12.12.2016 um 03:11 schrieb Mike Horvath:

> "Shutdown Warning: The maximum gradient found was 32.504, but
> max_gradient of the isosurface was set to 100.000. Adjust max_gradient
> to get a faster rendering of the isosurface."
> 
> According to this, max_gradient setting is not the problem, right?

Right.


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From: clipka
Subject: Re: Mysterious vanishing isosurface
Date: 12 Dec 2016 03:27:24
Message: <584e191c@news.povray.org>
Am 12.12.2016 um 04:09 schrieb Mike Horvath:
> On 12/8/2016 9:36 PM, Mike Horvath wrote:
>> If I rotate the camera 90 degrees around the x axis, the isosurface
>> disappears.
>>
>> Mike
> 
> I'm not sure why, but increasing the contained_by box fixed the problem.
> I used:
> 
>     contained_by
>     {
>         box {-1,1}
>     }
> 
> instead of:
> 
>     contained_by
>     {
>         box {0,1}
>     }

Maybe your functions have numeric instabilities near x=0, y=0 or z=0;
choosing a bounding box that does not coincide with these values would
drastically reduce the chance of the isosurface alhorithm hitting those
locations exactly, and it might now just skip over that ditch.


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From: William F Pokorny
Subject: Re: Mysterious vanishing isosurface
Date: 12 Dec 2016 13:57:13
Message: <584eacb9$1@news.povray.org>
On 12/11/2016 05:35 PM, clipka wrote:
> Am 11.12.2016 um 15:09 schrieb William F Pokorny:
>
>> A suggesting is trying the isosurface coded in your scene at a rotations
>> around where it is breaking up, at a low resolution, no aa+, area light,
>> etc., as
>>
>> isosurface {
>> }
>>
>> not used by reference (github #114 (#113 is related)), so you get some
>> idea what the max gradient really is and how it is changing.
>
> Thanks for bringing this report and analysis up again; I had wondered
> recently why my own toying-around with Mike's isosurfaces didn't prompt
> any max gradient warnings, but didn't take the time to investigate.
>
> I've just published a new version that supersedes the offending
> mechanism with something smarter, and should again report the max
> gradient as expected, for each and every isosurface actually rendered,
> yet aggregating the results for any clones.
>
> https://github.com/POV-Ray/povray/releases/tag/v3.7.1-alpha.8913469
>
This update will be very useful to me. Thanks much! :-)

Bill P.


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