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Hi,
I am quite new to povray and was wondering inf somebody could advice me how to
solve the following problem (hope it's not too trivial...):
I have a transparent object created with a sphere_sweep and some light sources
around. The problem is that the transparent object (a helix - see attachment)
produces solid/strongly reflecting solid sections normal to the sweep. I guess
these are not supposed to be there and I was wondering if there is a way to get
rid of them.
Thanks in advance,
Rolf
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Attachments:
Download 'spline_question.pov.txt' (3 KB)
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On 06/05/2015 03:52 AM, Rolf Umbach wrote:
> I have a transparent object created with a sphere_sweep and some light sources
> around. The problem is that the transparent object (a helix - see attachment)
> produces solid/strongly reflecting solid sections normal to the sweep. I guess
> these are not supposed to be there and I was wondering if there is a way to get
> rid of them.
Which version of POV-Ray are you using? I get vastly different results
depending on which version.
The sphere_sweep object is known to be buggy, especially with cubic
splines. But again, the bugs are different depending on the version of
POV-Ray.
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Cousin Ricky <ric### [at] yahoo com> wrote:
> On 06/05/2015 03:52 AM, Rolf Umbach wrote:
> > I have a transparent object created with a sphere_sweep and some light sources
> > around. The problem is that the transparent object (a helix - see attachment)
> > produces solid/strongly reflecting solid sections normal to the sweep. I guess
> > these are not supposed to be there and I was wondering if there is a way to get
> > rid of them.
>
> Which version of POV-Ray are you using? I get vastly different results
> depending on which version.
>
> The sphere_sweep object is known to be buggy, especially with cubic
> splines. But again, the bugs are different depending on the version of
> POV-Ray.
Hi,
I am currently running version 3.7. Is there a specific version you would
recommend to get rid of this bug or should I just try all (the more recent ones)
of them?
In any case, thanks for the quick reply!
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On 06/05/2015 10:08 AM, Rolf Umbach wrote:
> I am currently running version 3.7. Is there a specific version you would
> recommend to get rid of this bug or should I just try all (the more recent ones)
> of them?
POV-Ray 3.7 is fine. Note that it is strongly recommended that you put
a #version statement at the top of all your scene description files.
The file umbach-spline_question-3.7.png is my result from the 3.7
render. Does it show the problem you have?
I was unable to get rid of the artifacts. My best suggestion is to
download the SphereSweep module from the Object Collection, put the line
#include "spheresweep.inc" near the top of your scene file, and delete
the sphere_sweep object in your code, replacing it with:
#local Radii = array [2] { 0.05, r }
#local CtrlPts = array [points]
#local CtrlPts[0] = <0,0,0>;
#for (pt, 1, points - 1)
#local CtrlPts[pt] =
<R*cos(pt*P+ph+ph_tot_), pt*L, R*cos(pt*P+ph_tot_)>;
#end
SphereSweep_Approx (SSWP_CUBIC_SPLINE, CtrlPts, Radii, 5, 0)
You will get a warning about the spline feature. Ignore it.
The SphereSweep module can be downloaded at:
http://lib.povray.org/searchcollection/index2.php?objectName=SphereSweep&contributorTag=Cousin%20Ricky
My result is the file umbach-spline_question-sswp.png. Because you are
using 3.7, I felt free to use a #for instead of a #while. There are
bright areas where the coils are normal to the camera, but this is due
to the longer trace path through the emitting media, rather than a bug
of any sort.
I also replaced the union in macro emission_3 with a merge, to eliminate
the dark spot where the cone joins the coil. Although the POV-Ray
documentation doesn't recommend merge with sphere_sweep objects, it does
not appear to cause any problems in this case.
________________________
I have a few other suggestions for best practices that are unrelated to
your problem:
- As I mentioned above, always put a #version at the top of every
scene description file. (You should have received a warning about
this during your render.)
- 0.0 is not a valid value for roughness. (You should have received
a warning about this during your render.) Since your specular
value is also 0.0, the roughness statement is unnecessary anyway.
- User-defined identifiers should have at least one uppercase letter,
although this is not enforced. This recommendation is to prevent
possible conflicts with new keywords in a future version of
POV-Ray. (Some POVers have already been burned by this.)
- Variables that are temporary to a macro should be declared with
#local to prevent namespace collisions. Although POV-Ray has some
regrettable loopholes which make this far from foolproof, it is a
general good programming practice.
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Attachments:
Download 'umbach-spline_question-3.7.png' (13 KB)
Download 'umbach-spline_question-sswp.png' (12 KB)
Preview of image 'umbach-spline_question-3.7.png'
Preview of image 'umbach-spline_question-sswp.png'
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Hi,
Thank you very (!) much for your help. Your fix worked beautifully. Also, I
appreciate the general suggestions and will try to follow them in the future.
All the best and thanks again,
Rolf
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