[Radiance-general] 答复: Generate sky-matrix by using TMY weather data

[Germán Molina Larrain]

Hello Clarence,

I am not sure if I completely understood your question, but I think I can
help a bit understand what changed between  3 and 5 phases.

The three-phase method factorizes the DC matrix into three matrices ( DC =
VxTxD ), where T is the BSDF of a shading device. This helps changing T
without having to re-ray-trace, which is the slow process we want to avoid.
Despite being fast,, the Daylight Matrix (the D part in VTD) assumes the
sun to be spread in three or four patches of the sky (thus, Sarith's
comment regarding most values exept 3-4 being zeros for each hour), which
is unrealistic. The sun is not diffuse and big, but direct and small (0.533
degrees, which explains the "-5 0.533" part on the gendaymtx command),
which is why you substract this "big diffuse sun" and replace it by a
"small direct" sun.

Hope that helps!

2017-11-27 11:12 GMT-03:00 Wang Clarence <wangjuncwz at hotmail.com>:

> Thanks for replying.
>
> It seems that the .smx files are fine. But there is another question.
>
> When I combine the sun-matrix smx file with cds.mtx for direct sun
> coefficient simulation , which is the third part of the five-phase methods,
> the final data of cds.ill will be very small. Besides, since we use the
> data rendered by executing three phase method minus the data of direct
> solar part and plus the direct sun coefficient for rendering data of five
> phase method, the data of some measure  points which are close to the
> window rendering by five phase will be twice or  three times lower than
> that by three phase.
>
> So what is the actual difference of data between three phase and five
> phase? Are the data rendering by five phase definitely similar to that by
> three phase?
>
> Thanks,
>
> Clarence
> ------------------------------
> *发件人:* Sarith Subramaniam <sarith at psu.edu>
> *发送时间:* 2017年11月27日 5:50
> *收件人:* Radiance general discussion
> *主题:* Re: [Radiance-general] Generate sky-matrix by using TMY weather data
>
>
> Hi Clarence,
>
>
> If by null you are implying zeros, then the generated files are fine. Your
> first gendaymtx command ( -m 1 -d) will generate a sky matrix that is
> almost entirely zeros except for radiation values in 3-4 patches per hour
> during day-time.  The second gendaymtx command (-m 2 -5 0.533 -d) will
> generate a file that contains radiation values only in a single patch per
> hour. If the direct-normal radiation data for a particular hour is zero,
> then the radiation values in all the patches for that hour in direct-sky
> matrix and sun-matrix will be zero as well.
>
>
>
> Sarith
>
>
>
> On 11/26/2017 08:26 PM, Wang Clarence wrote:
>
> Dear all,
>
> When I created direct-only sky-matrix and sun-matrix of Hong Kong region
> by using commands "epw2wea" and "gendaymtx", the results seemed weird. The
> data of .smx file I rendered almost were null, so was the data of New York
> City . I had no ideas about its correctness.  Anyone could help me out of
> confusion?
>
> #Generate a direct-only sky-matrix for the sun coefficient calculation.
> #epw2wea weather/CHN_Hong.Kong.SAR.450070_CityUHK.epw weather/HK.wea
> #gendaymtx -m 1 -d weather/HK.wea > skyVectors/HKd.smx
>
> #Generate a sun-matrix for the sun coefficient calculation.
> #epw2wea weather/CHN_Hong.Kong.SAR.450070_CityUHK.epw weather/HK.wea
> #gendaymtx -m 2 -5 0.533 -d weather/HK.wea > skyVectors/HKsun.smx
>
> Thanks in advance.
>
> Best,
>
> Clarence
>
>
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