[Radiance-general] Help analyzing/calibrating a Radiance model to match simulated and measured illuminance

[Ehsan M.Vazifeh]

Hi Vaib,

There is a simple solution also to check if the errors caused by the
distribution of the diffuse or not. pick up the data for vertical
irradiance sensor and compare them to virtual sensors in Radiance. then if
there is similar trends as your result, you can infer that using gendaylit
model you cant get better performance as you already have.

Cheers,
Ehsan


On Tue, May 13, 2014 at 12:31 PM, Ehsan M.Vazifeh <em.vazifeh at gmail.com>wrote:

> Dear Vaib,
>
> I will prepare sky files based on sky scanner measurements for the period
> you mentioned in your presentation.
>
> The reason you get acceptable values for horizontal irradiance outside is
> that gendaylit is based on direct and diffuse data therefore you will get
> similar values in simulation. As Lars also mentioned distribution of
> diffuse is an-isotropic specially in case of breaking clouds. So after I
> send you the files please re-simulate again and let us know if you see any
> improvement in interior sensors values in comparison to the measured values.
>
> Cheers,
> Ehsan
>
>
> On Tue, May 13, 2014 at 11:52 AM, Lars Grobe <grobe at gmx.net> wrote:
>
>> Dear Vaib,
>>
>> thank you for sharing the presenatation with us!
>>
>> After a quick look at it, one potential source for the observed mismatch
>> may be the sky luminance distributions. You use a model of the sky, which
>> has a rather complex luminance distribution, based on only diffuse
>> horizontal and direct normal illuminance. These to values tell you little
>> about the luminance distribution not within the narrow angle obtained by
>> the sun, instead you use a theoretical model to reconstruct the
>> distribution. This means that for sunny sky conditions, when you know where
>> a huge fraction of luminous flux entering your scene is coming from (you
>> measure it and you know the sun position), you have a good estimate on the
>> sky distribution - while especially for sky conditions where the
>> distribution is far from uniform, but mostly diffuse, you really do
>> guess-work. E.g. clouds tend to give you a rather high variance in real
>> world, but get approximated as a smooth distribution with the sky models
>> you use.
>>
>> The sky models you use with the measured illuminance readings were ment
>> to be used for annual simulations. The generated distributions match the
>> average over a year. For single time-steps, which is what you compare, I
>> would expect deviations.
>>
>> Cheers, Lars.
>>
>>   Hello everyone!
>>
>> May I request you to please give some insight on the study I did to match
>> simulated and measured illuminance.
>>
>> Draft report: http://bit.ly/1nCpjU3
>>
>> Please have a look at the report.
>>
>> In this draft report I have tried to explain the model, and results using
>> different statistics. Also I have highlighted some areas in the time-series
>> graph, where the model is systematically (occurring during the same time)
>> under-estimating the illuminance. I don't know why?
>>
>> Do you think, there is still some scope of fine-tuning the model, or the
>> systematic error is uncertain to hypothesize?
>>
>> Do you think the results correlate well enough with other similar
>> benchmark daylight studies that used Radiance?
>>
>> I observed that the model correlates better in the case of "observed
>> sunny sky" as compared to "observed cloudy sky." But I couldn't understand
>> the reason behind this. ?
>>
>> Request you to please ask me if I missed to provide any info. about the
>> model.
>>
>> Thank you in anticipation.
>>
>> Best regards,
>> Vaib
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>
>
>
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