[Radiance-general] Sun too close to zenith

Gregory J. Ward gregoryjward at gmail.com
Wed Dec 7 23:39:28 CET 2005

Hi Rob,

I'm not exactly sure why I put this in there, it was so long ago.  I  
may have simply been duplicating someone else's algorithm, or I may  
have found problems related to the sun at zenith.  The whole sky  
distribution is normalized to the zenith value, so having the sun too  
near could be a problem, or it might have been paranoia on my part.

You can try removing lines 218-225 in gensky.c and recompiling without:

	if (!overcast && altitude > 87.*PI/180.) {
"%s: warning - sun too close to zenith, reducing altitude to 87  
"# warning - sun too close to zenith, reducing altitude to 87 degrees 
		altitude = 87.*PI/180.;

Try a few data points where the sun is at the zenith and see what  


> From: Rob Guglielmetti <rpg at rumblestrip.org>
> Date: December 7, 2005 1:59:46 PM PST
> Hi all,
> I'm using Francesco Anselmo's "radmap" script to generate some  
> annual skies for a fairly low latitude, and for a portion of the  
> summer gensky throws me a warning: "sun too close to zenith,  
> reducing altitude to 87 degrees".  This adjustment creates a slight  
> "bump" in the summertime corner of the analemma when you view a  
> hemispherical fisheye projection of the annual sun positions.  (The  
> sun positions are being generated by the script, which is getting  
> its info from an epw weather file.)
> What is the cause for gensky relocating my suns to 87 degrees?
> - Rob Guglielmetti

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