POV-Ray : Newsgroups : povray.beta-test : v3.8b2. height_field input values at 0.0 not clean. : Re: v3.8b2. height_field input values at 0.0 not clean. Server Time
14 Apr 2024 22:33:48 EDT (-0400)
  Re: v3.8b2. height_field input values at 0.0 not clean.  
From: William F Pokorny
Date: 18 Feb 2023 16:46:21
Message: <63f1472d$1@news.povray.org>
On 2/18/23 14:50, Kenneth wrote:
> So from these stats and results, my*guess*  is that there could be a very slight
> 'bias'(?) in the HF creation code-- or function-to-HF process? -- whereby the HF
> is not actually from 0-1, but (0 minus a small value) to (1 minus the small
> value.) OR, the same with the color_map mechanism. Although, the abrupt 'jumps'
> between .0000152 and .0000153 are puzzling

Interesting results and I think on the right track for some of what is 
unique about height_field bounding. What you see with the sudden large 
jump on that last subtraction is the out of bounds ramp wave value re-map.

For the smaller jumps. Internally, and probably due the original 
image_map only usage, the max 3d size we can have is 2^16 a side - 
HF_VAL is an unsigned short int. Vertically this means we are working in 
a best resolution of 1/2^16 steps = 0.00001525...  This lines up with 
the values where you see abrupt change in extents and that's kinda cool.

The bounds tracking is done at least in part in terms of doubles during 
calculation and where a value of HFIELD_OFFSET (currently 0.001) is 
subtracted from the lowest value per side and added to the greatest 
value on the top side. After the at double calculation, the result is 
converted back to HF_VAL.

Because that 0.001 isn't a multiple of the 16bits of resolution I 
believe there must be some value snapping going on during the double to 
HF_VAL conversion.

That's as far as I got before bailing out.

In looking at your results I'm not at all sure why the max extent values 
for x and z are all zero? The HF max extent should be 1 or larger for x 
and z (always I think if not scaled) ?

Bill P.


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