# gensky result different from that in, Axel's 	tutorial

**URL:** <https://discourse.radiance-online.org/t/gensky-result-different-from-that-in-axels-tutorial/3476>\
**Category:** radiance-general\
**Created:** [June 24, 2010, 2:11pm UTC](https://discourse.radiance-online.org/t/gensky-result-different-from-that-in-axels-tutorial/3476 "2010-06-24T14:11:43Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![Ji\_ZHANG](https://discourse.radiance-online.org/user_avatar/discourse.radiance-online.org/ji_zhang/32/563_2.png) [@Ji\_ZHANG](https://discourse.radiance-online.org/u/Ji_ZHANG)\
**Post date:** [June 24, 2010, 2:11pm UTC](https://discourse.radiance-online.org/t/gensky-result-different-from-that-in-axels-tutorial/3476/1 "2010-06-24T14:11:43Z")

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Thank you very much indeed, Axel and Greg!

> **···**
>
> On Thu, Jun 24, 2010 at 12:36 AM, Greg Ward \<gregoryjward@gmail.com\> wrote:
> 
> > Just a side-note: the turbidity factor is \_only\_ used by gensky to  
> > estimate the zenith luminance. If the horizontal irradiance or zenith  
> > radiance is given using -B or -b (respectively), turbidity is ignored.
> > 
> > Cheers,  
> > -Greg
> > 
> > From: Axel Jacobs \<jacobs.axel@gmail.com\>
> > 
> > > Date: June 23, 2010 8:27:12 AM PDT
> > > 
> > > Hi Ji Zhang
> > > 
> > > \> So, Which output is the correct one? What might causes the  
> > > \> differences?
> > > 
> > > The Radiance Tutorial must be about ten years old now. I keep updating it,  
> > > fixing small typos and inconsistencies, but have not felt the need to  
> > > reflect the recent changes to gensky's turbidity.
> > > 
> > > Both, CIE clear and overcast are extremes that are fairly unlikely to  
> > > occur in reality. As Greg said, you really need to feed in measurements, and  
> > > also have a good guess at the turbidity if you are concerned about accuracy.  
> > > If you can supply diffuse and direct irradiation, you might want to use  
> > > gendaylit instead.
> > > 
> > > Axel
> > 
> > \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_  
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> 
> --  
> ZHANG Ji 张冀 (PhD) :: Research Fellow :: Centre for Sustainable Asian Cities  
> :: School of Design and Environment :: National University of Singapore :: 4  
> Architecture Drive, Singapore, 117566 :: Contact: 65-6516 5046 :: Email:  
> sdezj@nus.edu.sg