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This is a series of images showing some problems I encountered when making an
hourglass.
The first one consists of a lathe object shaped into a bulb, referenced with a
negative scale component to create a hourglass shape then a scaled down version
(0.995) is differenced from it. You can see banding which looks to me as if the
glass does not have a uniform thickness.
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Attachments:
Download 'hourglass01e1_0000.jpg' (63 KB)
Preview of image 'hourglass01e1_0000.jpg'
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"Stephen" <mcavoys_AT_aolDOT.com> wrote:
> This is a series of images showing some problems I encountered when making an
> hourglass.
> The first one consists of a lathe object shaped into a bulb, referenced with a
> negative scale component to create a hourglass shape then a scaled down version
> (0.995) is differenced from it. You can see banding which looks to me as if the
> glass does not have a uniform thickness.
So I then created a second lathe object, making sure that it was inside the
first and that the thickness was as constant as I could make it then referenced
it to make the hourglass. Now there looks like there is flaring at the join.
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Attachments:
Download 'hourglass03a_0000.jpg' (79 KB)
Preview of image 'hourglass03a_0000.jpg'
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"Stephen" <mcavoys_AT_aolDOT.com> wrote:
>
> So I then created a second lathe object, making sure that it was inside the
> first and that the thickness was as constant as I could make it then referenced
> it to make the hourglass. Now there looks like there is flaring at the join.
The final two images are closeups of the join area. The first unfinished one
(12.5 hours) shows what looks like a disc around the join and the second is the
same scene with an opaque material
One image at a time, it seems
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Attachments:
Download 'hourglass03b1_0000.jpg' (58 KB)
Preview of image 'hourglass03b1_0000.jpg'
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"Stephen" <mcavoys_AT_aolDOT.com> wrote:
> "Stephen" <mcavoys_AT_aolDOT.com> wrote:
>
> >
> > So I then created a second lathe object, making sure that it was inside the
> > first and that the thickness was as constant as I could make it then referenced
> > it to make the hourglass. Now there looks like there is flaring at the join.
>
> The final two images are closeups of the join area. The first unfinished one
> (12.5 hours) shows what looks like a disc around the join and the second is the
> same scene with an opaque material
>
> One image at a time, it seems
Now the opaque one
Post a reply to this message
Attachments:
Download 'hourglass03b1a_0001.jpg' (23 KB)
Preview of image 'hourglass03b1a_0001.jpg'
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I am frankly at a loss for a solution, but some questions impose
themselves maybe.
1) are the two ends overlapping?
2) the ends do not seem to be exactly parallel, (outer) edges flowing
smoothly into one another.
3) could the effect be due to refraction?
Thomas
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Thomas de Groot <tho### [at] degroot org> wrote:
> I am frankly at a loss for a solution, but some questions impose
> themselves maybe.
>
> 1) are the two ends overlapping?
>
> 2) the ends do not seem to be exactly parallel, (outer) edges flowing
> smoothly into one another.
>
> 3) could the effect be due to refraction?
>
> Thomas
The lathes were built with the lowest point on the ground plane then rotated 90
degrees. The other bulb is mirrored so the edges should be coincidental.
Although I can see that there is not a smooth transition between them in the
opaque image. The inner lathe extends past the outer one and the highest level
CSG is a merge so there should be no internal surfaces.
Well the IOR is quite high for glass, greater than 1.5 IIRC. I was wondering
about internal reflections as well.
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"Stephen" <mcavoys_AT_aolDOT.com> wrote:
> "Stephen" <mcavoys_AT_aolDOT.com> wrote:
> > "Stephen" <mcavoys_AT_aolDOT.com> wrote:
> >
> > >
> > > So I then created a second lathe object, making sure that it was inside the
> > > first and that the thickness was as constant as I could make it then referenced
> > > it to make the hourglass. Now there looks like there is flaring at the join.
> >
> > The final two images are closeups of the join area. The first unfinished one
> > (12.5 hours) shows what looks like a disc around the join and the second is the
> > same scene with an opaque material
> >
> > One image at a time, it seems
>
> Now the opaque one
I suggest you render a cross-section, preferably highlighting the cutaway
surface (i.e. intersection { <hourglass> plane { -z, 0 pigment { rgb x } } } ).
But I think most of your problems come from using a spline type where you can't
control the gradient where the mirrored bulbs meet. So either don't mirror them,
and use a curve that describes both bulbs of the hourglass, or use a
bezier_spline and place the control point tangentially to the desired curve to
get a smooth transition.
Or you could download the source for my "Sands Of Time" IRTC entry:
http://exether.free.fr/irtc/index.php?sub=pg2004&lang=en&year=2004&month=8&typ=S&mrk=C
;)
--
Tek
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On 17/10/2012 4:31 PM, Tek wrote:
> I suggest you render a cross-section, preferably highlighting the cutaway
> surface (i.e. intersection { <hourglass> plane { -z, 0 pigment { rgb x } } } ).
>
Yes, I think that is the way to go. It has been ages since I have used
SORs or Lathes and I am quite lazy. :-)
> But I think most of your problems come from using a spline type where you can't
> control the gradient where the mirrored bulbs meet. So either don't mirror them,
> and use a curve that describes both bulbs of the hourglass, or use a
> bezier_spline and place the control point tangentially to the desired curve to
> get a smooth transition.
>
I was using a cubic curve but my endpoint wasn't making making the joint
take the right angle.
> Or you could download the source for my "Sands Of Time" IRTC entry:
>
http://exether.free.fr/irtc/index.php?sub=pg2004&lang=en&year=2004&month=8&typ=S&mrk=C
> ;)
Strange that you say that, Norbert suggested it too.
I found it interesting that you could use so few points and get such a
good curve.
--
Regards
Stephen
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On 17/10/2012 3:16 PM, Thomas de Groot wrote:
> I am frankly at a loss for a solution, but some questions impose
> themselves maybe.
>
> 1) are the two ends overlapping?
>
I checked and they were. :-(
Even after correcting that. The gold ring was still there but much
diminished.
> 2) the ends do not seem to be exactly parallel, (outer) edges flowing
> smoothly into one another.
>
Too true, I used a poor end point.
> 3) could the effect be due to refraction?
>
Yes, I think so. When I commented out the sand. The ring was still there
but much less visible.
Ah! Well. Back to the drawing board.
--
Regards
Stephen
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You could try to reshape the curve in the center so it is not
a hard edge but rather a little rounded. If this is two pieces
joined together you'll want the end to have vertical/horizontal
tangents. BTW you can post more than one image when using a
newsreader such as Thunderbird.
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