POV-Ray : Newsgroups : povray.binaries.images : Granite_21 - the final macro : Re: Granite_21 - the final macro Server Time
26 Sep 2022 03:20:25 EDT (-0400)
  Re: Granite_21 - the final macro  
From: Samuel B 
Date: 18 Sep 2021 17:05:00
Message: <web.6146538cb21f010ccb705ca46e741498@news.povray.org>
"Bald Eagle" <cre### [at] netscapenet> wrote:
> "Samuel B." <stb### [at] hotmailcom> wrote:
> In the lower right area of the image you can
> > see the numbers "4.913 x 4.913 x 5.4045" which are probably the dimensions of
> > the cell. The numbers "90 90 120" are the angles. But how to convert these to
> > proper planes? All my attempts have failed. There is probably a basic solution
> > and I'm just over-complicating things...
>
> I agree that those are the dimensions and angles.
> But they are the angles of the unit cell, and ATM I fail to see how you need
> them.

I think they merely point to the angles and dimensions one would need when
converting HKL indices into proper plane normals. For a cubic system, this would
be straightforward, but for a hexagonal system, something else is needed. I
tried shearing/skewing & scaling cubic coords to produce proper results, but as
said before, I had no luck.

> What I DO see, is that you have numerical triplets, indicating the hkl indices.
> I believe that you can simply use those numbers as the normal vectors for all of
> the face planes.  Maybe there's a way to display them with greater precision.

There is no greater precision. Attached is an image showing the table of HKL
indices of a basic quartz crystal. When you click on any number field, you'll
find it's just an integer. (Except for the distance values, of course.) If I'm
not mistaken, this is because the HKL system only works for the intended
coordinate spaces (aka unit cells).

> Still not sure about the offset, but maybe once you get the ball rolling, some
> light will be shed on that aspect of the data.

Not sure what you mean. The plane offsets? Those are given by the aforementioned
fourth value, "distance."

> And that's all I have before 1st coffee.   :D

Drink 'em if you've got 'em! ;)

Sam


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