On 2018-02-09 10:28 PM (-4), Mike Horvath wrote:
> The fuzzy circles don't look so great. I don't know if anything can be
> done to improve them however. In video games, stars are often reduced to
> 1 pixel. But I don't think in POVray there's an easy way to make a star
> exactly 1 pixel big. Maybe with some trigonometry?

Yes, of course they can be improved!  The purpose of the demo was merely 
to demonstrate how to use the data.  I consider attempting a realistic 
sky beyond the scope of the demo.

This works if you are representing the stars as actual objects:

----------[BEGIN CODE]----------
#version 3.7;

global_settings { assumed_gamma 1 }

#declare Cam_angle = 60;
#declare RSky = 10000; // arbitrary distance to the stars
#declare R = RSky * tan (radians (Cam_angle / 2)) / image_width;

camera
{ location 1.64 * y
   look_at <0.5, 2.64, 2.5>
   angle Cam_angle
}

plane { y, 0 pigment { checker } }

#include "brightstar5.inc"

#default { finish { ambient 0 diffuse 0 emission 1 } }
union
{ #for (I, 0, BSC5_N - 1)
     #if (BSC5_Data [I] [BSC5_HD] != BSC5_NO_DATA)
       sphere
       { RSky * y, R
         pigment { rgb BSC5_fn_Brightness (BSC5_Data [I] [BSC5_MAG], 0) }
         rotate
         < 90 - BSC5_Data [I] [BSC5_DEC],
           -15 * BSC5_Data [I] [BSC5_RA],
           0
         >
       }
     #end
   #end
   rotate <0, 120, 71.7>
}
-----------[END CODE]-----------

I disregarded image_height in the formula because the POV-Ray camera 
considers only image_width for its field angle.  Also note that if the 
camera is significantly distant from the origin, you will need to make 
appropriate adjustments.

Note that with a diameter of 1 pixel, an adaptive anti-aliasing trace 
will miss quite a few stars.  To avoid this, you'll need to either use 
+A0.0 (slow), or use a diameter slightly larger than 1 pixel (times 
sqrt(2) should do).  As far as using boxes instead of spheres, I don't 
think it would be worth the effort.

If Orion looks strangely oriented in the above code, it's because I'm 
stargazing from the northeast Caribbean.

Yes, there is some distortion as you move away from the center of the 
image, as explained in the knowledge base:
   http://wiki.povray.org/content/Knowledgebase:Misconceptions#Topic_3

The orthographic camera will preserve the star shape, but the star 
positions will still be distorted, for the reason you learned in 4th 
grade geography.  Also, the orthographic camera would be quite awkward 
to use if you are rendering, say, a landscape.

A sky sphere would use a different formula, but the math would be similar.

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