JeffBTX nous illumina en ce 2009-05-30 12:28 -->
> Please refer to this thread in the New Users section:
>
http://news.povray.org/povray.newusers/thread/%3Cweb.4a2091fa9ea5e81c2c1590090%40news.povray.org%3E/
> 
> The first post is:
> http://news.povray.org/web.4a2091fa9ea5e81c2c1590090%40news.povray.org
> 
> Message header:
> From: JeffBTX
> Subject: DF3 / interpolation question
> Date: 30 May 2009 02:00:01
> 
> Basically I am getting artifacts from DF3 files. Alain suggested a possible
> solution; fill empty spaces with 1's instead of 0's. I tried it... the problem
> was alleviated somewhat. I am still getting severe artifacts if a voxel is
> placed EXACTLY at the corner of a media cube, so I "backed the voxel off" into
> the cube away from the corner a little. I'm still getting artifacts.
> 
> ====================
> Here is the code that I used to display the DF3:
> ====================
> 
> include "colors.inc"
> 
> camera {location <0,1.5,-1.5> look_at <0,0,0>}
> 
> light_source {<10,0,-10> rgb 1}
> 
> // plane {z, 10 pigment {Gray50} hollow }
> 
> box {0, 1
> 
>   texture {
>     pigment {rgbt 1}
>   }
> 
>   interior {
> 
>     media {
> 
> //      emission 1*3
> //      absorption 1*5
> //      scattering {1, White*3 extinction 1}
> 
> 
>       density {
>         density_file df3 "ts10.df3" interpolate 0
>       }
> 
>     }
> 
>   }
>   hollow
>   translate -0.5
>   rotate <0,45,0>
> }
> ====================
> 
> As you can see, one can comment out / uncomment any or all of the three media
> types. For absorption media to show, there is a gray plane behind the media
> cube that can be un-commented-out.
> 
> The three green cylinders help to orient the viewer.
> 
> ====================
> 
> 
> The attachment is a screenshot of the data inside the DF3 (a hexdump). This is a
> 10x10x10 DF3; but I am still having the problem with a 100x100x100; I used a 10x
> DF3 to show the voxel better. The header is indicated by green boxes, the voxel
> is indicated by a red box. The DF3 is of the proper filesize and I think it was
> constructed properly; 10*10*10+6 = 1006 bytes.
> 
> As you can see, the offset of the voxel is at 075h. That puts the voxel *AT* the
> second coordinate away from the forward, left, lower corner. The coord is XYZ =
> 2,2,2; subtracting 1 to bring into the range of 0 to 9 is 1,1,1; and then the
> offset is 1 + (1*10) + (1*10*10) = 111, + 6 (for the header) is 117, and in hex
> that is 075h.
> 
> As Alain suggested, I filled the blank DF3 with 01 instead of 00 before I
> altered it for the voxel.
> 
> In further posts I will try to post a .ZIP of the DF3, and a screenshot of
> renderings that displays the problem (this will be the first time I have tried
> to post attachments, so we will see if this works...)
> 
> 
> ------------------------------------------------------------------------
> 
Good news!

There are NO artefacts when using version 3.7 beta 32 and interpolate 2.
Interpolate 0 is NO interpolation. You only see the voxel.
Interpolate 1 is linear interpolation. The voxel becomes fuzzy.
With 3.6.1 and interpolate 2, there are HUGE artefacts. Making the container 
larger don't help, in fact, the result gets worst. Also, if you enlarge the 
container, you also need to increase the samples value a LOT. Adding 0.1 all 
around and you need samples 20, at least!

Also, DON'T increase the intervals value!
I just tested samples 300 VS. intervals 30 samples 10.
My "normalised" times are:
intervals 30 samples 10: 1 (100% of the time)
samples 300: 0.787 (78.7% of the time)

samples 300 gives much smoother results, even if they are still uncorrect.

The documentations are WRONG about the default values used. They are:
method 3
intervals 1
samples 3

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