Hi Joe,
Thank you for the references.
The HDR image by default is co-planar with the x and z axis with its surface normal pointing in the negative y direction. You'll need to translate the image so that its surface normal is pointed down along the negative z axis and rotate it so that North is up when looking up towards zenith.
The groundglow description is actually not necessary and has no effect. If you wanted to define the ground for inclusion in a scene you could use the following:
void glow groundglow
0
0
4 .15 .15 .15 0 #(.15 .15 .15 = RGB values for the ground material)
groundglow source ground
0
0
4 0 0 -1 180
I too have been getting lower values than the measured global horizontal illuminance. I think the suggestions made made by Rob and Greg about using mksource and adjusting the subtended angle of the solar source may be the solution. Not sure yet how to implement the latter but I will certainly keep you posted.
Cheers,
Chris
On Jun 30, 2014, at 10:26 PM, Joe Smith <the.oat.cracker at gmail.com> wrote:
> Hi Chris,
>
> Thank you very much for your reply, especially for reminding me the conversion of the unit between foot candela and lux!
>
> May I ask the following questions?
>
> 1. why the hdr fisheye image needs to be rotated along x axis for 90 degrees and along z axis for 180 degrees? using the fisheye.cal file as reference when defining the colorpict "skypict"?
>
> 2. why "skypict is used as a modifier to define the "glow" material "groundglow"? I thought usually this position is set as "void"
>
>
> Using your approach, I tried some other hdr image provided by your project, and it seems the global horizontal illuminance is always underestimated as compared to the one reported in the csv file.
>
> rubbing my head about this issue, and advices are greatly appreciated!
>
> Regards,
> Joe
>
>
>
> On Tue, Jul 1, 2014 at 3:06 AM, Christian Humann <chris at christianhumann.com> wrote:
> Hi Joe,
>
> The global values in the CSV file are in footcandles so you will need to multiply them by 10.76 in order to get Lux.
>
> Also, you'll need to add a source description for the sun in order to get the solar contribution as the camera sensor can not capture the intensity of the sun for the HDR image. Essentially the HDR image allows you to get a close approximation of the global diffuse value. I use gendaylit (see below) to generate the sun and sky scene. You can get the altitude, azimuth, direct-normal-illuminance and diffuse-horizontal-illuminance from the CSV file (be sure to multiply the latter two values by 10.76 to translate them from footcandles to Lux for input into Gendaylit). Also be sure to adjust your 'rtrace' results by dividing by 10.76 to get footcandles if you want to compare to the global-horizontal-illuminacne readings in the CSV file.
>
> ########Sun and Sky scene -----> global.rad
> !gendaylit -ang 45.41 85.92 -w -O 0 -L 80463.28 19916.76 | xform -e -rz 0
> void colorpict skypict
> 11 red green blue 140621_1530.hdr fisheye.cal fish_u fish_v -rx 90 -rz 180
> 0
> 0
>
> skypict glow skyglow
> 0
> 0
> 4 1 1 1 1
>
> skyglow source sky
> 0
> 0
> 4 0 0 1 180
>
> skypict glow groundglow
> 0
> 0
> 4 1 1 1 0
>
> groundglow source ground
> 0
> 0
> 4 0 0 -1 180
> #########
> # 3. the cmd.sh file
> oconv ./global.rad > ./scene_empty.oct
>
> echo '0 0 0 0 0 1' | rtrace -I -h -w -ab 1 -oov ./scene_empty.oct > ./results_position_irradiance_RGB_wm2.txt
>
> cat ./results_position_irradiance_RGB_wm2.txt | rcalc -e '$1=179*(0.265*$4+0.670*$5+0.065*$6)/10.76' > ./results_illuminance_lux.txt
> ##########
>
> When I run the above I get a global horizontal illuminance value from 'rtrace' of approx. 6900 footcandles. The photometer gave a reading of 7176 footcandles.
>
>
> I'm still working my brain around all this as well and hope that these discussions will foster a better understanding of how to use the HDR images for the highest level of accuracy possible.
>
> Hope this helps.
>
> Best,
> Chris
>
>
>
>
> On Jun 28, 2014, at 10:06 AM, Joe Smith <the.oat.cracker at gmail.com> wrote:
>
>> 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.
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>> Hunter Douglas Chile S.A.
>> Celular +569 89224445
>>
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