[Radiance-general] HDR Sky Camera @ LBNL's Flexlab

Sat Jun 28 10:06:48 PDT 2014

Hi, I found 2 references and did a test to generate HDR image-based
rendering, steps are explained below.

But I'm still rubbing my head to understand how the Cartesian coordinates
or the postion vector of a point on the sky is transformed as UV
coordinates of the fisheye image as shown in the "angmap.cal" file. So,
advices are greatly appreciated!

Thanks!
Joe

References:
1. Debevec, P. (2002). Image-based lighting. IEEE Computer Graphics and
Applications, 22(2), 26-34. doi: 10.1109/38.988744
2. Au, P. Y. P. (2013). HDR Luminance Measurement: Comparing real and
simulated data. (Master of Building Science Thesis), Victoria University of
Wellington.

Steps:
Step1. prepare the following 6 files and put them in the same folder

#### 1.1 geom.rad ################################################
red_plastic sphere ball
0
0
4 2 2 0.5 0.5

steel sphere ball1
0
0
4 2 -2 0.5 0.5

gold sphere ball2
0
0
4 -2 -2 0.5 0.5

white_matte sphere ball3
0
0
4 -2 2 0.5 0.5

crystal sphere ball4
0
0
4 0 0 1 1

!genbox gray_plastic pedestal_top 8 8 0.5 | xform -t -4 -4 -0.5

#### 1.2 materials.mat ################################################
void plastic red_plastic
0
0
5 .7 .1 .1 .06 .1

void metal steel
0
0
5 0.6 0.62 0.68 1 0

void metal gold
0
0
5 0.75 0.55 0.25 0.85 0.2

void plastic white_matte
0
0
5 .8 .8 .8 0 0

void dielectric crystal
0
0
5 .5 .5 .5 1.5 0

void plastic black_matte
0
0
5 .02 .02 .02 .00 .00

void plastic gray_plastic
0
0
5 0.25 0.25 0.25 0.06 0.0

#### 1.3 sky_and_ground.rad ################################################
void colorpict hdr_image
7 red green blue 140621_1530.hdr angmap.cal u v
0
0

hdr_image glow sky_glow
0
0
4 1 1 1 0

sky_glow source HDR_sky
0
0
4 0 0 1 180

# ground
void glow ground_glow
0
0
4 1 1 1 0

ground_glow source ground
0
0
4 0 0 -1 180

#### 1.4 angmap.cal ################################################
{
angmap.cal

Convert from directions in the world (Dx, Dy, Dz) into (u,v)
coordinates on the light probe image

+z is up (toward top of sphere, i.e. the zenith)
+y is North
}

d = sqrt(Dx*Dx + Dy*Dy);

r = acos(Dz)/PI;

u = 0.5 - Dx/d * r;
v = 0.5 + Dy/d * r;

#### 1.5 view.vf ################################################
# looking towards east
#rvu -vtv -vp -12 0 0.5 -vd 1 0 0 -vu 0 0 1 -vh 60 -vv 40
# looking towards west
#rvu -vtv -vp 12 0 0.5 -vd -1 0 0 -vu 0 0 1 -vh 60 -vv 40
# looking towards north
rvu -vtv -vp 0 -12 0.5 -vd 0 1 0 -vu 0 0 1 -vh 60 -vv 40
# looking towards south
#rvu -vtv -vp 0 12 0.5 -vd 0 -1 0 -vu 0 0 1 -vh 60 -vv 40

#### 1.6 cmd.sh ################################################
oconv ./materials.mat ./sky_and_ground.rad ./geom.rad > ./scene.oct

rvu -vf ./view.vf ./scene.oct

#ximage ./sky.hdr

rpict -x 2400 -y 2400 -t 30 -ab 1 -ar 50000 -aa 0.08 -ad 128 -as 64 -st 0
-lw 0 -lr 8 -vf ./view.vf ./scene.oct > ./image.hdr

pfilt -1 -x /3 -y /3 -r 1 ./image.hdr > ./image_filtered.hdr

Step2. put the 140621_1530.hdr file provided by LBNL (
http://flexskycam.lbl.gov) in the same folder

Step3. run the cmd.sh batch file to produce the rendering

On Sat, Jun 28, 2014 at 7:28 AM, Andrew McNeil <amcneil at lbl.gov> wrote:

> Hi All,
>
> I haven't done any testing myself, I wanted to make the data available
> right away so that others could tinker too (and maybe make it easier for
> me).
>
> Joe - You're correct that the HDR sky image essentially replaces the
> skyfunc modifier, here's a thread where Kyle was doing the same thing:
> http://www.radiance-online.org/pipermail/radiance-general/2012-October/008962.html
>
>
> Rob - In a clear sky condition our HDR images won't capture the full
> luminance of the sun. Mksource would be helpful to zero out the pixels, but
> the source that it makes won't be useful without adjusting the radiance of
> the source to match that of the sun.
>
> Best,
> Andy
>
>
>
>
> On Fri, Jun 27, 2014 at 2:58 PM, Rob Guglielmetti <
> rob.guglielmetti at gmail.com> wrote:
>
>> Hi German, and everyone else. Certainly one could use these HDR images to
>> generate sky vectors and apply them to daylight coefficients for a given
>> model(s). Greg Ward has created a cool tool called mksource to facilitate
>> this process in Radiance, identifying small, intense pixels in the image;
>> creating and placing Radiance light sources in their stead, and zeroing the
>> pixels to avoid double counting.
>>
>> Considerations:
>> - Capturing the true (full) dynamic range of an exterior scene with
>> direct sun is difficult.
>> - Using locally-captured HDR images for daylight availability analysis is
>> statistically dubious. Granted, so is using TMY data, for different
>> reasons. This is why I changed the title of this list to "considerations",
>> from "problems". =)
>>
>>
>>
>>
>>
>> On Fri, Jun 27, 2014 at 3:38 PM, CHI-German Molina <gmolina at hdlao.com>
>> wrote:
>>
>>> Wow, I have been thinking on doing this for a while... although I have
>>> no idea where to start from.
>>>
>>> Is it possible to calculate the Daylight Coefficients of the building;
>>> and use the HDR image to generate sky vectors and calculate different
>>> options for optimizing daylighting?
>>>
>>> I am picturing a computer that, every 5 minutes, calculate the sky
>>> vector, computes the interior lighting conditions, and simulates the
>>> different lighting options performing a whole-building lighting control
>>> with no photo sensors. Even more, maybe a whole neighborhood could use the
>>> same camera. Nonsense?
>>>
>>> Thanks for sharing!
>>>
>>>
>>> 2014-06-27 0:59 GMT-04:00 Joe Smith <the.oat.cracker at gmail.com>:
>>>
>>>> Hi, Andy, thanks for sharing LBNL's sky mapping experiment!
>>>>
>>>> Can you kindly advice on resources that elaborate on how to use HDR sky
>>>> image for daylight simulation? Does it involve specifying the HDR image,
>>>> rather than a "skyfunc", as the material identifier for the sky geometry?
>>>> How is the pixel value of a given point on the HDR image converted to
>>>> luminance value of the corresponding position on the sky?
>>>>
>>>> Thanks!
>>>> - Joe
>>>>
>>>> Andrew McNeil <amcneil at lbl.gov>于2014年6月27日星期五写道：
>>>>
>>>> Hi Everyone,
>>>>>
>>>>> LBNL has installed an HDR sky camera at our new FLEXLAB site:
>>>>> http://flexskycam.lbl.gov. I've uploaded sample data, including hdr
>>>>> images and csv datafiles, recorded by the camera for three days over the
>>>>> past week( clear, partly cloudy and overcast). We're happy to share more
>>>>> data with other researchers and daylight practitioners (but we don't have
>>>>> much to offer yet).
>>>>>
>>>>> The images can be mapped to a Radiance sky for simulation under real
>>>>> sky conditions. I have not used the sky HDR images yet, myself, so if
>>>>> anybody uses them successfully please report back and share what you've
>>>>> done!
>>>>>
>>>>> Questions about the camera hardware and capabilities should be
>>>>> directed to Chris Humann at Terrestrial Light.
>>>>>
>>>>> Best,
>>>>> Andy
>>>>>
>>>>
>>>> _______________________________________________
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>>>>
>>>
>>>
>>> --
>>> *Germán Molina L.*
>>> Ingeniero Trainee
>>> Hunter Douglas Chile S.A.
>>> Celular +569 89224445
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