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"Bald Eagle" <cre### [at] netscape net> wrote:
> I was exploring some unrelated things (as usual), and I found an interesting
> shadow clock that was easy to model
>
>
https://www.dezeen.com/2015/10/23/breaded-escalope-touch-shadow-clock-vienna-design-week-2015/
>
> And then I was noticing how the sun came into my apartment, and thinking back on
> a solar energy model I made a few years ago, and Ingo's sunpos.inc file, and I
> recalled that an ordinary watch can be used as a makeshift compass.
>
> Orient the hour hand to point at the sun (accurately done with a blade of grass
> to cast a shadow across the hour hand) and then divide the angle between the
> hour hand and the 12:00 mark. That's roughly South.
>
> I wanted to see how it worked, and get an idea of how far off it would be.
>
> So naturally I modeled it in POV-Ray :)
>
> Seems to work ok, and be off by +/- 30 degrees - dead on at noon.
Interesting animation. Not sure why or how you did the sine wave type thing but
since 1 hour equals 15 degrees longitude that would cause some inaccuracy if not
near the middle of a time zone. And of course Daylight Savings Time, if in areas
using that.
As usual, I was making your description more complicated than it is. Shadow
across hour hand... then I realized I was making matters worse by imagining the
minute hand to be the hour hand! Found a wikiHow page telling about it but only
made matters worse before I realized the drawings weren't exactly right, then it
finally made sense.
http://www.wikihow.com/Use-an-Analog-Watch-as-a-Compass
I like that wall shadow clock. Someone made a comment about it not showing the
hour and minute differently, would have to guess. Not too much of a problem if
you know the general time of day already but overlapping would cause trouble.
Solution might be to use 2 different color lights.
Bob
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