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Am 02.01.2019 um 08:18 schrieb COMPATT:
> Even when I use an accuracy of 0.0001 I continue to get moire patterns at the
> "terminator" of my planet when the light rays would be striking at a very low
> angle to the isosurface I am not getting a max gradient error but I am using a
> very high resolution greyscale topographic image map any ideas on how to make
> them go away completely? I am not interested in using a mesh instead I would
> like to do this just using the image map as an isosurface function. Not sure
> what to include in this post to help you help me so please let me know what
> other info will be helpful
As Bald Eagle already suggests, you need a much lower accuracy setting.
In isosurfaces, intersection points are not computed in a single step
using a formula, but rather via a bisection-based iterative algorithm
that narrows down the location of the intersection point until it is at
most `accuracy` units off the mathematically correct surface.
Due to how the bisection works, you essentially get "terracing" on your
isosurface, and the pattern you see are the terrace steps casting shadows.
You need to reduce `accuracy` to a value low enough that the height of
the terrace steps falls within POV-Ray's precision bounds for shadow
calculations. 1e-6 will do for the scene you posted.
(The moire pattern is a moire pattern indeed, but in this case does not
arise from interaction between image content and the pixel structure of
the image, but from the interaction between the shape and the bisection
intervals. Not sure how you got anti-aliasing to affect it, but I
suspect you may have toyed with other settings as well and simply forgot.)
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