POV-Ray : Newsgroups : povray.text.scene-files : ObjectToDF3Example.pov for creating DF3 files with povray directly. Server Time
21 Jul 2024 13:36:14 EDT (-0400)
  ObjectToDF3Example.pov for creating DF3 files with povray directly. (Message 1 to 1 of 1)  
From: William F Pokorny
Subject: ObjectToDF3Example.pov for creating DF3 files with povray directly.
Date: 22 Sep 2013 21:27:52
Message: <523f9918$1@news.povray.org>
I worked up a povray only solution for creating df3 files using objects 
grouped by color in the 0-1 unit space & the relatively new 
ARRAYS_WriteDF3() of arrays.inc.

As part of the attached code I have documented several DF3 issues I've 
found the hard way and I'll duplicate that information here so it 
eventually shows up in searches.

Notes on DF3 files in general no matter how used. Someday I'll have the 
time to put together a tutorial with images. Perhaps one or more explain 
why folks sometimes struggle with DF3 files.

1) Today we have 3 DF3 density file interpolation techniques 0,1 and 2. 

    - The 0 interpolation type is voxel centered.

    - The 1 & 2 types are vertice centered, shifting everything lower 
1/2 voxel.

      - If mixing the two types this is important to understand, 
especially with smaller DF3 files where the shift is relatively more 
substantial. Functions in isosurfaces or patterns can re-align.

2) Interpolation type 2 rings / wobbles when there are any surface 
protrusions, or when say a plane of one value has a larger or smaller 
value inserted in that plane. If using type 2 for anything you want to 
be numerically stable, use multiple single value coincident DF3 files. I 
tend not to use option 2 at all.

    a) Further, if the ring goes below 0 or above 1 it gets clamped at 0 
or 1.

3) Keep your DF3 data away from the array edges for interpolation types 
1 & 2.

    - Both techniques implement edge wrapping / handling which mangle 
things near the DF3 edges.

    - I'm now adding a buffer of 5 df3 voxels around meaningful inner 

Bill P.

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