[Radiance-general] Zenith Luminance from rvu

[Vaib]

Hi Rob,

I missed to mentioned that I tried -s a (auto) also. Also I tried to get
the peak value from pextrem. But I got skeptical as these values were about
100 times more (for sunny sky) than what I saw in some research papers; and
the image was just one color. :)

That's why I came back to manually tracing the brightest pixel approach.

Can you please elaborate on the "log 2" scale approach ? Thank you for your
time!

BEst regards,
Vaib



On 23 May 2014 23:56, Guglielmetti, Robert <Robert.Guglielmetti at nrel.gov>wrote:

> Hi Vaib,
>
> Falsecolor now has an "auto" option to the –s parameter, which will
> automatically set the top of the scale to the peak value found in the
> image. Note the peak value will not necessarily be at the zenith (which,
> yes, is where the vector 0,0,1 points to in a hemispherical fisheye view).
>
> I also find that for other than overcast skies, using a logarithmic scale
> (-log 2) is very useful for getting the most value out of a falsecolor
> representation of a sky's luminous distribution.
>
> On 5/23/14, 12:14 PM, "Vaib" <vaibhavjain.co at gmail.com<mailto:
> vaibhavjain.co at gmail.com>> wrote:
>
> Hello Everyone,
>
> I am trying to create falsecolor fish-eye image of just the sky. For that
> I am using:
>
> rpict -vta -vp 0 0 0 -vd 0 0 1 -vu 0 1 0 -vh 180 -vv 180 sky.oct |
> falsecolor -s XYZ -l cd/m2 > sky.hdr
>
> Dr.Mardaljevic in his dissertation said to set -s argument of falsecolor
> close to the Zenith luminance, that can be obtained by rvu's trace command.
>
> To get the Zenith luminance, I am tracing the ray (using rvu) that is
> approximately at the centre of the image created with the above view
> parameters, and setting this ray's luminance value as the -s option of
> falsecolor.
>
> Is this the right way to show/cover the whole luminance spectrum in the
> sky ? (It doesn't look so in the image..)
>
> Or shall I trace the ray at the apparently at the brightest pixel ? (by
> reducing the exposure, and figuring out that pixel)
>
> I think the term Zenith Luminance may mean the luminance at the centre of
> the sky, but I must take your opinion before concluding. Thank you!
>
> Best regards,
> Vaib
>
>
>
>
>
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