POV-Ray : Newsgroups : povray.binaries.images : Spherical displacement map : Re: Spherical displacement map Server Time: 28 Sep 2020 16:05:58 GMT
  Re: Spherical displacement map  
From: Bald Eagle
Date: 21 Jul 2020 11:00:00
Le_Forgeron <jgr### [at] freefr> wrote:

> acos( min( y / length, 1) ) : the clipping is done for the north pole,
> but not the south pole (-1)
> what about "acos(max(min(y/length, 1),-1)) ?

Thanks Jerome, it was a good suggestion, but the hole is still there.

I'm also concerned that although I may happen upon a "solution" that looks nice
graphically, it will be numerically wrong.  And that's because I'm going to be
using these calculations to "look up" the altitude on the rectangular elevation
map in order to construct planet tiles that are in the right position (as
closely as possible using this method and the data available).

I'm also curious as to why I got I got a core dump with no clipping, and no core
dump with half-clipping, if the domain input was the underlying issue.  Because
without the min(), then I'd be running into the same problem that I was
imagining was happening, only with the opposite sign.

And I'm not even sure that the domain was out range now that we're back into
this again.  (it's early, before coffee, and it's HOT)
(I mean, can y ever exceed the vector length to give a quotient exceeding
I DO have my isosurface contained by a sphere instead of a box - maybe that has
something to do with it - I will check later this afternoon.

I really do have a knack for finding these little hidden problems...

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