[Radiance-general] DGP on 172 fish-eye image

[Jan Wienold]

Hi Raquel,

I agree that the outer 8° contribute only a little to the vertical 
illuminance. The solid angle of that section is around 0.44sr (which is 
around 7% of the total) and the cosinus for this flat angle of incidence 
is also very low (in average around 0.07). so the overall impact of the 
outer 8 degree is less than 0.5%, assuming the luminances in that area 
are comparable to the average of the image .

Regarding the "filling" option in evalglare: this was implemented, 
because there was a group using a fish-eye lens, where the projected 
circle was larger in y-direction than the CCD-array. This function 
"fills up" the missing parts with the last known value vertically. You 
cannot use it in my opinion to fill up missing "ring" areas (to fill up 
between 172° to 180°). Actually I could implement such a feature, but 
due to the low impact I don't think it is necessary and so far no other 
users were missing such a feature.

Are you really sure you have a equidistant-projecting lens with 172°?  
The equidistant types are  much less frequent on the market - most 
lenses cover 180° or more.
If you have a equi-solidangle fish-eye lens, you should correct the 
projection as well.

What you should definitely check is how close you get between measured 
illuminance with the sensor and the calculated value from evalglare. If 
you have a deviation there, you have a problem in the calibration 
(because the influence of the outer 8% is really negligible, so you 
should nearly match the value ).

BTW: Are you coming to the academic forum of Velux May2nd? As far as I 
know, there are at least three other PhD students there dealing with 
HDR-cameras, daylight and glare and as far as I heard there are still 
free spots.  I will be there as well.

best
Jan



On 03/15/2017 10:31 AM, Raquel Viula wrote:
> Hi Alstan,
> That’s great to know, thank you. Yes, I have vertical eye illuminance 
> measurements. I think it’s probably a good idea to estimate what the 
> error might be via simulation.
>
> Best Regards
>
> Raquel
>
>
> *Raquel Viula*
>
> PhD candidate
>
>
> *TUDelft | Faculty of Architecture and the Built Environment |*
>
> Architectural Engineering and Technology
>
> Julianalaan 134, 2628 BL Delft, The Netherlands | P.O. Box 5043 2600 
> GA Delft
>
>
> From: "J. Alstan Jakubiec" <alstan at jakubiec.net 
> <mailto:alstan at jakubiec.net>>
> Reply-To: Radiance general discussion 
> <radiance-general at radiance-online.org 
> <mailto:radiance-general at radiance-online.org>>
> Date: Wednesday 15 March 2017 06:18
> To: <radiance-general at radiance-online.org 
> <mailto:radiance-general at radiance-online.org>>
> Subject: Re: [Radiance-general] DGP on 172 fish-eye image
>
> Hi Raquel,
>
> I would say yes. Just make sure that the view in the HDR header is 
> appropriate or you specify it inline: evalglare -vta -vv 172 -vh 172 
> image.hdr
>
> This may slightly underestimate vertical eye illuminance calculated by 
> the software, skewing your results a bit; however, 172 is close enough 
> to 180 in terms of view angle that the error is likely minimal. Still, 
> if you have vertical eye illuminance measurements, supply them inline 
> with the -i flag as well.
>
> Best,
>
> Alstan
>
>
> On 3/14/2017 9:40 PM, Raquel Viula wrote:
>> Dear all,
>> I have a question regarding Evalglare. Hopefully this is the right 
>> mailing list to ask.
>> Can DGP be calculated for a -vta fish-eye photo capture that has a 
>> view angle of 172 degrees? The manual says that Evalglare can be run 
>> for an image cut horizontally given an externally measured vertical 
>> eye illuminance and Y max and Y min coordinates but does not mention 
>> the possibility of using an image that is also cut vertically, or 
>> shall I say, all around.
>> Thank you for your help.
>>
>> Best Regards
>>
>> Raquel
>>
>>
>> *Raquel Viula*
>>
>> PhD candidate
>>
>>
>> *TUDelft | Faculty of Architecture and the Built Environment |*
>>
>> Architectural Engineering and Technology
>>
>> Julianalaan 134, 2628 BL Delft, The Netherlands | P.O. Box 5043 2600 
>> GA Delft
>>
>>
>>
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>> Radiance-general mailing list
>> Radiance-general at radiance-online.orghttp://www.radiance-online.org/mailman/listinfo/radiance-general
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-- 
Dr.-Ing.  Jan Wienold
Ecole Polytechnique Fédérale de Lausanne (EPFL)
EPFL ENAC IA LIPID

http://people.epfl.ch/jan.wienold
LE 1 111 (Office)
Phone    +41 21 69 30849

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