[Radiance-general] Uniform sky

[Thomas Bleicher]

Vera

This sounds like you are trying to create something like an "ambient
occlusion" or "clay rendering"; the closer you are to an object the more
obstructed the view of the sky is and so the ground gets darker.

You can indeed create this using a uniform sky but you have to use "-ab 1"
for your rendering or the sky will not contribute to the scene. The "no
light sources found" warning comes up because a "glow" material that is
used for the sky technically does not count as a light "source" Radiance.

If you plan to use the rendering for analysis you can set the sky
brightness to a known quantity so that the rendering can be interpreted as
an absolute value of the obstruction of the sky. I think John Mardaljevic
wrote down the math for this in the Rendering with Radiance chapter on
skies/daylight. You should also add "-av 0 0 0" or the added ambient value
will skew your results.

Regards,
Thomas




On Sun, May 4, 2014 at 9:50 PM, Vera Liu <lizzielyh at gmail.com> wrote:

> Hi Joe,
> For the ground truth I'm thinking about just the surface lit by the light
> at each pixel without any ray tracing. Basically, the RGB of the surface as
> it would be if it were directly lit by the light without any
> interreflections or specularities. I figured that a uniform sky would do
> the trick.
>
> Best,
> Vera
>
>
> On Sun, May 4, 2014 at 7:08 PM, Joe Smith <the.oat.cracker at gmail.com>wrote:
>
>> Hi, Vera, may I ask what you mean by "ground truth pixel value"?
>>
>> - JS
>>
>> Vera Liu <lizzielyh at gmail.com>于2014年5月5日星期一写道：
>>
>> Hi Radiance experts,
>>> I want to get the ground truth pixel values of a scene generated by
>>> radiance and I figured the best way is to use a uniform sky where the sky
>>> it's 1,1,1...everywhere. The way I'm currently using is by specifying a sun
>>> !gensky 4 1 12 +s -a 40 -o 98 -m 105
>>> skyfunc glow sky_glow
>>> 0
>>> 0
>>> 4 1 1 1 0
>>> sky_glow source sky
>>> 0
>>> 0
>>> 4 0 0 1 180
>>>
>>> This results in shadows in the final scene. I found that -u option or -c
>>> option can give me a uniform cloudy sky and maybe give me the ground truth
>>> values. I tried both of them but always get 'no lighting source warning'
>>> and a very dark scene when I try to use rpict and pfilt on the .oct
>>> generated. I think I might be understanding something wrong. Could you
>>> please give me a hint on this? The two options I tried are:
>>> !gensky 3 20 12 -a 40 -o 98 -m 105 -u -B 100
>>> and
>>> !gensky -ang 45 0 -c -b 1
>>>
>>> Thank you very much!
>>> Best,
>>> Vera
>>>
>>
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