[Radiance-general] Radiance-general Digest, Vol 125, Issue 3

[Andrew McNeil]

Hi Maria,
How are you handling the sun in you sunny sky? Do you have a source
separate from the hdr sky image? How have you set the Radiance of the sun?
If I had to guess, I'd say your sun is too bright.
Andy



On Wed, Jul 2, 2014 at 3:31 PM, María Beatriz Piderit <beapiderit at gmail.com>
wrote:

> Dear Kyle,
> I downloaded the file that was in the link you attached for rendering hdr
> sky images. I tried it with two of my images, the first was a clear sky and
> the other one was an overcast sky.
> With the overcast sky I didn't had any problems, it rendered fine,
> although the clear sky image render didn't come out well. There are two
> issues: the first is that in the HDR images the sky appears really dark,
> and in the TIFF image the sky looks good but the ground disappears.
> Could you give me some tips to improve the clear sky images? Have you had
> this problem when dealing with a clear sky render?
> This is the link where you can see the results:
> https://www.dropbox.com/sh/ujhiskn9ohks3vt/AAAjkOyAis6_MfCEHfXwwalea
>
> Best,
>
>  M. Beatriz Piderit M.
> Arquitecta UBB, MA, PhD UC Louvain
>
> Departamento Diseño y Teoría de la Arquitectura
> Universidad del Bio-Bio Concepción, Chile
>
>
> El 01-07-2014, a las 19:10, radiance-general-request at radiance-online.org
> escribió:
>
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> Today's Topics:
>
>   1. Re: HDR Sky Camera @ LBNL's Flexlab (Kyle Konis)
>
>
> ----------------------------------------------------------------------
>
> Message: 1
> Date: Tue, 1 Jul 2014 16:10:29 -0700
> From: Kyle Konis <kskonis at gmail.com>
> To: Radiance general discussion <radiance-general at radiance-online.org>
> Subject: Re: [Radiance-general] HDR Sky Camera @ LBNL's Flexlab
> Message-ID:
> <CAAzVHq2LfEF7k1q2Asexzh4Du-jeTJd_pfqB4SUZ4BO1x=hiXQ at mail.gmail.com>
> Content-Type: text/plain; charset="utf-8"
>
> Following up here, (and on the referenced thread from about a year ago), i
> did succeed in rendering some simple Radiance objects with HDR skies.
>
> I have uploaded an example video here with the LBNL Skycam images (June 21,
> 2014 until about 10:40 AM) which was all I could process during the world
> cup match:
>
> http://performance-and-form.com/projects/rendering-digital-objects-with-high-dynamic-range-hdr-sky-images/
>
> Thanks are due to Coralie Cauwerts for corresponding to provide me with the
> proper .cal file for mapping hemispherical (rather than spherical) images.
>
> The skies are used to render a chrome sphere sitting on a pedestal. You can
> tell it is not a real object because it is outside for several hours and no
> birds sit or poop on it. (Good luck HDR Skycam ! )
>
> I have zipped all the files used to make the video and put them on the page
> for download, as well as a few experiments i have made in manipulating
> surfaces (either transmission or shading) in response to sky data from
> Portland, Oregon using a Canon A570 with Stereo Data Maker used to automate
> bracketed image acquisition (i have a plan to post the details for that, as
> it is a very low-cost < $80 approach and will get to it).
>
> let me know (offline) if there are issues downloading or executing the
> files,
>
> best,
>
> -Kyle
>
> -----------------------------------------------
> Kyle Konis, AIA, Ph.D
> Assistant Professor
> School of Architecture, WAH 204
> University of Southern California
> Los Angeles, CA 90089-0291
> http://arch.usc.edu/faculty/kkonis
> -----------------------------------------------
>
>
>
>
>
>
>
> On Tue, Jul 1, 2014 at 8:52 AM, Christian Humann <
> chris at christianhumann.com>
> wrote:
>
> 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>?2014?6?27???????
>
> 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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>
>
> --
> *Germ?n Molina L.*
> Ingeniero Trainee
> Hunter Douglas Chile S.A.
> Celular +569 89224445
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