[Radiance-general] Ray-tracing with Radiance
Germán Molina Larrain
germolinal at gmail.com
Mon Aug 10 06:19:18 PDT 2015
Ikrima,
Strictly speaking, Radiance always use ray-tracing. Whenever you call
RPICT, RTRACE or RCONTRIB, there will always be a ray-tracing simulation
performed. However, when you want to perform annual simulations, you will
want to do as few ray-tracing simulations as possible since they take time.
RTRACE, for example, is a method used to calculate the illuminance or
luminance of a point (sensor) in a static scene. Doing this for a whole
year would require 8760 or more RTRACE calls, which means 8760 or more
ray-tracing simulations, which is slow.
Accordingly, Daysim (which uses the 2-phase method) runs one ray-tracing
simulation that calculates the Daylight Coefficient matrix (this can be
done in pure radiance by using RCONTRIB). This matrix relates the sensors
(workplane?) in the scene with the sky, mich means that you can modify the
sky and quickly evaluate illuminance in the same points. This allows
performing annual simulations fast (only the sky changes in a static annual
simulation). 3 and 5 phase method are extensions to this that allow also
modifying the CFSs in the scene.
Hope that clarify a little bit.
Best,
Germán
2015-08-10 8:51 GMT-03:00 Ikrima Amaireh <ezxia at nottingham.ac.uk>:
> Hello Robert,
> Hello all,
>
> As some of you may remember, I am trying to model a set of CFS to compare
> their effect on indoor horizontal illuminance of a room. So far, I have
> been advised by you for several stages, which really helped me a lot for
> better understanding of radiance and how it works.
>
> Now, I have a question about how I use ray-tracing method in radiance? Is
> it similar to the way explained through the following attachment? As here,
> calculations are run using Radiance engine but Ecotect or Daysim interface
> (for geometry modelling and material assignment).
>
> Document:
> http://web.mit.edu/sustainabledesignlab/projects/TeachingResources/GettingStartedwithEcotectRadianceDaysim.pdf
>
> I hope if you can kindly advise me on that asap, please?
>
>
> Best regards
> Ikrima
>
>
>
> -----Original Message-----
> From: radiance-general-request at radiance-online.org [mailto:
> radiance-general-request at radiance-online.org]
> Sent: 12 July 2015 20:37
> To: radiance-general at radiance-online.org
> Subject: Radiance-general Digest, Vol 137, Issue 12
>
> Send Radiance-general mailing list submissions to
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> Today's Topics:
>
> 1. Git for Windows and starting tutorials (Ikrima Amaireh)
>
>
> ----------------------------------------------------------------------
>
> Message: 1
> Date: Sun, 12 Jul 2015 20:36:19 +0100
> From: Ikrima Amaireh <ezxia at nottingham.ac.uk>
> To: "radiance-general at radiance-online.org"
> <radiance-general at radiance-online.org>
> Cc: Ikrima Amaireh <ezxia at nottingham.ac.uk>
> Subject: [Radiance-general] Git for Windows and starting tutorials
> Message-ID:
> <
> D697763F9F216044A99BC674C00561961358CA9C4C at EXCHANGE1.ad.nottingham.ac.uk>
>
> Content-Type: text/plain; charset="us-ascii"
>
> Hi Robert,
>
> Many thanks for your help.
>
> I have installed Git for Windows as you adviced :) Now, Before I start
> with 3 or 5-phase tutorials, I'm thinking to go through "radiance tutorial"
> (by Axel Jacobs) as a beginner with almost a shallow knowledge/experience
> of radiance. So, do recommend this (radiance tutorial would be enough to
> start with 3 or 5-phase methods and understanding of BSDF data approach,
> etc) or advice another tutorial/source for better understanding of radiance
> basics (using command prompt)?
>
> Many thanks again :)
>
> Regards
> Ikrima
>
>
>
> ------------------------------
>
> Message: 2
> Date: Fri, 10 Jul 2015 15:52:23 +0000
> From: "Guglielmetti, Robert" <Robert.Guglielmetti at nrel.gov>
> To: "radiance-general at radiance-online.org"
> <radiance-general at radiance-online.org>
> Subject: Re: [Radiance-general] Radiance-general Digest, Vol 137,
> Issue 8
> Message-ID: <D1C542EA.1AE88%Robert.Guglielmetti at nrel.gov>
> Content-Type: text/plain; charset="us-ascii"
>
> OK so it sounds like you first tried the Windows installer (presumably a
> NREL-provided one such as this:
> https://github.com/NREL/Radiance/releases/download/5.0.a.3/radiance-5.0.a-w
> in64.exe), and this most likely worked fine, you just had some issues
> actually *doing* anything with it. This is normal. =)
>
> I recommend you install Git for windows (https://msysgit.github.io/), as
> that will add a little BASH emulator in your Windows system. This way you
> can run most of the commands exactly as they appear in most of the
> tutorials out there that are written from a UNIX perspective (as you point
> out). If you run the "Git BASH shell" you will be able to try out all the
> multi-phase methods, use and generate BSDFs, etc. Once you have Git for
> Windows installed, head over to Andy McNeil's tutorials for 3- and 5-phase,
> fire up the Git BASH shell (it'll be in the Git program group in the
> Windows start menu), and get started!
>
> One thing to keep in mind is that when running any commands that
> read/write data (e.g. rcontrib), be sure to use ASCII format rather than
> float. Windows has issues with float data (among many other things).
>
> Good luck!
>
> - Rob
>
> On 7/10/15, 8:08 AM, "Ikrima Amaireh" <ezxia at nottingham.ac.uk> wrote:
>
> >Hi Robert,
> >
> >My PC is running on Windows 7 Enterprise.
> >Initially, I installed Radiance for Window using its installer but I
> >found that most of the tutorials are provided for pc with Linux and/or
> >Linux-like operating systems; So I had to install try learnix (that did
> >not work) and Ubuntu (also did not work)!
> >Finally, I tried to use Cygwin to run Radiance on Window OS. I could
> >install Cygwin (works fine), Xming (not sure if working) and Radiance
> >(not all its programs are working!).
> >
> >I'm a bit confused as I'm not sure if running Radiance on windows using
> >Cygwin will be enough for carrying my work. For example, can I work out
> >phases methods and generate BSDF data?
> >
> >I wish if you can help me to do that.
> >
> >Many thanks
> >ikrima
> >
> >
> >
> >------------------------------
> >
> >Message: 3
> >Date: Thu, 9 Jul 2015 16:44:49 +0000
> >From: "Guglielmetti, Robert" <Robert.Guglielmetti at nrel.gov>
> >To: "radiance-general at radiance-online.org"
> > <radiance-general at radiance-online.org>
> >Subject: Re: [Radiance-general] Could not install Radiance!!!
> >Message-ID: <D1C400AC.1ADAC%Robert.Guglielmetti at nrel.gov>
> >Content-Type: text/plain; charset="us-ascii"
> >
> >Hi Ikrima,
> >
> >We'll need a bit more info, here. What OS are you on? How are you
> >attempting to install it (using an installer, compiling from source, or
> >what)? What happens when you try??
> >
> >On 7/9/15, 10:38 AM, "Ikrima Amaireh" <ezxia at nottingham.ac.uk> wrote:
> >
> >>Hi all,
> >>
> >>After one a few weeks of trying, I could not manage to install
> >>radiance properly. I am almost disappointed! Please any help?
> >>
> >>Regards
> >>Ikrima
> >
> >
> >
> >
> >This message and any attachment are intended solely for the addressee
> >and may contain confidential information. If you have received this
> >message in error, please send it back to me, and immediately delete it.
> >
> >Please do not use, copy or disclose the information contained in this
> >message or in any attachment. Any views or opinions expressed by the
> >author of this email do not necessarily reflect the views of the
> >University of Nottingham.
> >
> >This message has been checked for viruses but the contents of an
> >attachment may still contain software viruses which could damage your
> >computer system, you are advised to perform your own checks. Email
> >communications with the University of Nottingham may be monitored as
> >permitted by UK legislation.
> >
> >
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>
>
>
>
> ------------------------------
>
> Message: 3
> Date: Fri, 10 Jul 2015 17:34:30 +0100
> From: Ikrima Amaireh <ezxia at nottingham.ac.uk>
> To: "radiance-general at radiance-online.org"
> <radiance-general at radiance-online.org>
> Cc: Ikrima Amaireh <ezxia at nottingham.ac.uk>
> Subject: [Radiance-general] Modelling CFS
> Message-ID:
> <
> D697763F9F216044A99BC674C00561961358CA9BAF at EXCHANGE1.ad.nottingham.ac.uk>
>
> Content-Type: text/plain; charset="us-ascii"
>
> Hi all,
>
> Thanks Robert and Larrain for your detailed replies, that helped me a lot.
>
> I would summarise here what I got form your appreciated replies, as
> following:
> - Radiance is convenient and best of tools to model daylighting due to its
> ray-tracing method.
> - 3 or 5-phases methods are used to facilitate the calculations.
> - Generating BSDF data is also used to facilitate these calculations but
> it is limited to Klems resolution of some CFS.
>
> Initially, I'm not planning to do annual calculations. It's just for
> specific hours of the day and the target is to produce a illuminance levels
> for indoor grid under different CFSs. Hence, according to my understanding
> from Larrain words, I can use either 2-phase or Ray-tracing methods. My
> question is how can I draw/define the CFS geometry and Space for these
> calculations? Is it similar to the way use in Ecotect/Radiance calculations?
>
> Regards
> Ikrima
>
>
> -----Original Message-----
> From: radiance-general-request at radiance-online.org [mailto:
> radiance-general-request at radiance-online.org]
> Sent: 09 July 2015 19:56
> To: radiance-general at radiance-online.org
> Subject: Radiance-general Digest, Vol 137, Issue 8
>
> Send Radiance-general mailing list submissions to
> radiance-general at radiance-online.org
>
> To subscribe or unsubscribe via the World Wide Web, visit
> http://www.radiance-online.org/mailman/listinfo/radiance-general
> or, via email, send a message with subject or body 'help' to
> radiance-general-request at radiance-online.org
>
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>
> When replying, please edit your Subject line so it is more specific than
> "Re: Contents of Radiance-general digest..."
>
>
> Today's Topics:
>
> 1. CFS with Radiance (Ikrima Amaireh)
> 2. Could not install Radiance!!! (Ikrima Amaireh)
> 3. Re: Could not install Radiance!!! (Guglielmetti, Robert)
> 4. Re: CFS with Radiance (Guglielmetti, Robert)
> 5. Re: CFS with Radiance (Germ?n Molina Larrain)
>
>
> ----------------------------------------------------------------------
>
> Message: 1
> Date: Thu, 9 Jul 2015 17:26:29 +0100
> From: Ikrima Amaireh <ezxia at nottingham.ac.uk>
> To: "radiance-general at radiance-online.org"
> <radiance-general at radiance-online.org>
> Cc: Ikrima Amaireh <ezxia at nottingham.ac.uk>
> Subject: [Radiance-general] CFS with Radiance
> Message-ID:
> <
> D697763F9F216044A99BC674C00561961358CA9710 at EXCHANGE1.ad.nottingham.ac.uk>
>
> Content-Type: text/plain; charset="us-ascii"
>
> Hi G. Larrain,
>
> Thanks for your detailed clarification (below).
>
> I wonder if you kindly can help me toward better understanding and
> answering the following:
>
> We agreed that for daylight modelling of spaces with CFS, Radiance is a
> suitable tool as it applies ray-tracing method. And for annual and/or
> climate-based daylight calculations, as calculation time becomes a critical
> factor, using BSDF data for CFS is highly recommended to tackle the task
> with radiance (using phases methods). However:
>
> - if someone needs to perform daylight calculations for given space with
> different CFS (different cases for comparison purposes) to get illumination
> levels for horizontal grid points (and not pictures nor scenes), is
> Radiance still the most convenient option?
> - is it still needed to use any of the phase methods (2, 3 or 5)?
> - most importantly, is it still needed to get BSDF data for CFS or just
> can model the detailed CFS in Radiance (and, if yes, how?)
>
>
> Many thanks for your kind help :)
>
> Regards
> Ikrima
>
>
> "Ikrima,
>
> I am going to try to build the puzzle of CFS, Phases, BSDF and
> calculations.... at least the way I understand it.
>
> *CFS* are those systems that, via interreflection or other light transport
> phenomena, redirect light (or solar radiation). Thus, in order to get a
> reliable result you will have to consider all the phenomena involved.
> Then, *common
> simple performance indexes*, such as the miss-used Shading Coefficient and
> the Aperture Percentage, *always loose a lot of information, trying to
> reduce all the complex behavior of a CFS to one single number*. We all know
> that venetian blinds are more "transparent" from certain viewing directions
> than from others, but these performance indexes do not tell you that.
>
> Now... Radiance can certainly perform calculations of spaces with CFS
> using its "common" Ray-tracing. However, this may be slow for some purposes
> (i.e.
> annual simulations and climate-based daylight modelling), and *this is why
> 2, 3 and 5 phase methods have been developed*. The *BSDF* representation, I
> would say, goes in the same direction... It allow summarizing all the
> bounces, reflections, refractions, etc. that occure withing the CFS in a
> single matrix or tensor.* By using BSDFs*, Radiance itself and other tools
> (i.e. EnergyPlus) can treat CFS as blackboxes, avoiding all the opcits
> within the system. A BSDF that uses the Klems Full representation has
> 21,045 numbers (instead of one, such as the Shading Coefficient).
>
> Being said all that, I would not trust a calculation method unless it can
> actually deal with the optics of a CFS that is drawn and/or it can use BSDF
> (or similar) information.
>
> Lets remember that a perforated screen, a venetian blind, a light
> diffusing device can all have a Shading Coefficient of 50%, but all of them
> will behave very differently. I made some presentations about this on my
> previous work (we sold complex Shading Devices), trying to promote the use
> of BSDF in EnergyPlus calculations... the differences (in solar heat gains)
> were more than considerable.
>
> I hope that someone else gives us his/her perspective on this topic...
> there are a lot of concepts that I might be misunderstanding.
>
> Best!"
>
>
>
>
> This message and any attachment are intended solely for the addressee and
> may contain confidential information. If you have received this message in
> error, please send it back to me, and immediately delete it.
>
> Please do not use, copy or disclose the information contained in this
> message or in any attachment. Any views or opinions expressed by the
> author of this email do not necessarily reflect the views of the University
> of Nottingham.
>
> This message has been checked for viruses but the contents of an
> attachment may still contain software viruses which could damage your
> computer system, you are advised to perform your own checks. Email
> communications with the University of Nottingham may be monitored as
> permitted by UK legislation.
>
>
>
>
> ------------------------------
>
> Message: 2
> Date: Thu, 9 Jul 2015 17:38:41 +0100
> From: Ikrima Amaireh <ezxia at nottingham.ac.uk>
> To: "radiance-general at radiance-online.org"
> <radiance-general at radiance-online.org>
> Cc: Ikrima Amaireh <ezxia at nottingham.ac.uk>
> Subject: [Radiance-general] Could not install Radiance!!!
> Message-ID:
> <
> D697763F9F216044A99BC674C00561961358CA9719 at EXCHANGE1.ad.nottingham.ac.uk>
>
> Content-Type: text/plain; charset="us-ascii"
>
> Hi all,
>
> After one a few weeks of trying, I could not manage to install radiance
> properly. I am almost disappointed! Please any help?
>
> Regards
> Ikrima
>
>
>
>
> This message and any attachment are intended solely for the addressee and
> may contain confidential information. If you have received this message in
> error, please send it back to me, and immediately delete it.
>
> Please do not use, copy or disclose the information contained in this
> message or in any attachment. Any views or opinions expressed by the
> author of this email do not necessarily reflect the views of the University
> of Nottingham.
>
> This message has been checked for viruses but the contents of an
> attachment may still contain software viruses which could damage your
> computer system, you are advised to perform your own checks. Email
> communications with the University of Nottingham may be monitored as
> permitted by UK legislation.
>
>
>
>
> ------------------------------
>
> Message: 3
> Date: Thu, 9 Jul 2015 16:44:49 +0000
> From: "Guglielmetti, Robert" <Robert.Guglielmetti at nrel.gov>
> To: "radiance-general at radiance-online.org"
> <radiance-general at radiance-online.org>
> Subject: Re: [Radiance-general] Could not install Radiance!!!
> Message-ID: <D1C400AC.1ADAC%Robert.Guglielmetti at nrel.gov>
> Content-Type: text/plain; charset="us-ascii"
>
> Hi Ikrima,
>
> We'll need a bit more info, here. What OS are you on? How are you
> attempting to install it (using an installer, compiling from source, or
> what)? What happens when you try??
>
> On 7/9/15, 10:38 AM, "Ikrima Amaireh" <ezxia at nottingham.ac.uk> wrote:
>
> >Hi all,
> >
> >After one a few weeks of trying, I could not manage to install radiance
> >properly. I am almost disappointed! Please any help?
> >
> >Regards
> >Ikrima
> >
> >
> >
> >
> >This message and any attachment are intended solely for the addressee
> >and may contain confidential information. If you have received this
> >message in error, please send it back to me, and immediately delete it.
> >
> >Please do not use, copy or disclose the information contained in this
> >message or in any attachment. Any views or opinions expressed by the
> >author of this email do not necessarily reflect the views of the
> >University of Nottingham.
> >
> >This message has been checked for viruses but the contents of an
> >attachment may still contain software viruses which could damage your
> >computer system, you are advised to perform your own checks. Email
> >communications with the University of Nottingham may be monitored as
> >permitted by UK legislation.
> >
> >
> >_______________________________________________
> >Radiance-general mailing list
> >Radiance-general at radiance-online.org
> >http://www.radiance-online.org/mailman/listinfo/radiance-general
>
>
>
>
> ------------------------------
>
> Message: 4
> Date: Thu, 9 Jul 2015 17:29:39 +0000
> From: "Guglielmetti, Robert" <Robert.Guglielmetti at nrel.gov>
> To: "radiance-general at radiance-online.org"
> <radiance-general at radiance-online.org>
> Subject: Re: [Radiance-general] CFS with Radiance
> Message-ID: <D1C40477.1ADCA%Robert.Guglielmetti at nrel.gov>
> Content-Type: text/plain; charset="us-ascii"
>
> Some very quick replies and clarifications within:
>
> On 7/9/15, 10:26 AM, "Ikrima Amaireh" <ezxia at nottingham.ac.uk> wrote:
>
> >Hi G. Larrain,
> >
> >Thanks for your detailed clarification (below).
> >
> >I wonder if you kindly can help me toward better understanding and
> >answering the following:
> >
> >We agreed that for daylight modelling of spaces with CFS, Radiance is a
> >suitable tool as it applies ray-tracing method. And for annual and/or
> >climate-based daylight calculations, as calculation time becomes a
> >critical factor, using BSDF data for CFS is highly recommended to
> >tackle the task with radiance (using phases methods). However:
>
>
> BSDF data in an annual simulation context is generally limited to Klems
> basis BSDF data, which may not be high enough resolution for some CFS. And
> the 5-phase method, which can circumvent this, is not necessarily "quick".
> This is all still very much a quandary and the newest daylight metrics
> have added confusion to all of this, IMO.
>
>
> >
> >- if someone needs to perform daylight calculations for given space
> >with different CFS (different cases for comparison purposes) to get
> >illumination levels for horizontal grid points (and not pictures nor
> >scenes), is Radiance still the most convenient option?
>
>
> Absolutely. The lack of an image-as-output requirement does not change the
> fact that ray tracing is a good/convenient algorithm option for daylight
> simulation problems, especially when dealing with diffusing media and CFS
> in general. BSDFs allow you to do lots of "what-ifs", relatively quickly,
> but are beholden to the limitations of the resolution of the BSDF.
>
>
> >- is it still needed to use any of the phase methods (2, 3 or 5)?
>
>
> Is what still needed? BSDF data? Ray tracing? I don't know of other
> lighting simulation tools that can employ the multiphase methods. I would
> say BSDF data is optional for 2-phase, required for 3-phase, and optional
> for 5-phase.
>
> >- most importantly, is it still needed to get BSDF data for CFS or just
> >can model the detailed CFS in Radiance (and, if yes, how?)
>
>
> Again I'm confused as to what "it" is. A couple of approaches are
> available to you in general. If you have a geometric model of the CFS you
> can use Radiance (genBSDF) to make a BSDF of the CFS and use that in a 3-
> or 5-phase context. However in an annual/climate-based simulation context,
> you will be stuck with a Klems basis BSDF and that will not be very good
> resolution for a lot of CFS; here you may want to use the 5-phase method
> and stick the actual CFS geometry in the building model.
>
> Some things to consider here are the photon map, now a part of Radiance
> proper, or using the 2-phase method where appropriate. By 2-phase method I
> mean generating a daylight matrix for your calculation points (or view),
> and modeling the window material as-is. If the "CFS" is a shade cloth, you
> can approximate that with a Radiance "trans". Same for translucent panels.
> With this single daylight matrix, you can throw a vector of sky matrices
> at it and get an annual climate-based result very quickly. Problem is, we
> want to do stuff to the windows, sometimes at the time step level, so:
>
> Blinds and compact daylight redirection devices (e.g. Lightlouver) are
> best represented as BSDF, and if most of the redirected flux is headed up
> and away from the points of interest, a Klems basis BSDF is good enough
> IMO. In these cases you could use the 3-phase method. Problem is when you
> have a BSDF for blinds, and you also want to simulate the blinds-up
> condition (i.e. clear, specularly transmitting glass). Using a Klems basis
> BSDF for this is sub-optimal. You end up needing to do two annual
> simulations, one as 2-phase for the clear glass scenario, and again as a
> 3-phase (with a blinds BSDF for the transmission matrix) for the blinds
> down condition. If you have a lot of different window groups, your
> simulation space can get large in a hurry. But it's still do-able and you
> can get results that tell a story you simply couldn't tell 5 years ago,
> informing the newest daylight metrics as well.
>
>
>
>
>
>
> ------------------------------
>
> Message: 5
> Date: Thu, 9 Jul 2015 15:56:11 -0300
> From: Germ?n Molina Larrain <germolinal at gmail.com>
> To: Radiance general discussion <radiance-general at radiance-online.org>
> Subject: Re: [Radiance-general] CFS with Radiance
> Message-ID:
> <CAF-iH4LSr=y12F1khTrHh6hnf-kS=EmaFuo8uWKvHqMs=
> FZL-Q at mail.gmail.com>
> Content-Type: text/plain; charset="utf-8"
>
> I must say that I agree with Rob, however, a short answer that might help.
>
> For evaluating illuminance levels in a space with different CFS you,
> strictly speaking, DO NOT HAVE TO do anything. You may choose between
> different methods that have some pros and cons.
>
>
> *ray-tracing*
>
> - Requires ray-tracing for each time-step and each system, which is slow
> (*four systems simulated annualy in an hourly basis --> 4*8760 = 35,040
> simulations*.)
> - As accurate as it gets, if options are defined correctly.
>
>
> *2 phase method*
>
> - Do not need the BSDF
> - Requires ray-tracing for each CFS (*4 systems --> 4 ray-tracing
> simulations*)
> - After ray-tracing, annual simulation is fast.
>
> *3-phase method:*
>
> - Requires BSDF data in KLEMS basis, which may be slow to compute,
> unless it can be exported from WINDOW, for example, or such data has
> already been calculated (the idea is to make a database, I think).
> - Does not really work well for specular systems (Klems patches are too
> big)
> - Requires 2 ray-tracing runs, always (*4 systems --> 2 ray-tracing
> simulations*)
> - After ray-tracing and BSDF calculation, annual simulation is fast
>
> *5-phase method:*
>
> - Requires BSDF data in KLEMS basis AND/OR Tensor tree format, which
> may be slow to compute, unless it can be exported from WINDOW, for
> example,
> or such data has already been calculated (the idea is to make a
> database, I
> think).
> - Works well for specular systems
> - Requires 4 ray-tracing runs + 1 for each system, always (*4 systems
> --> 4+1 = 5 ray-tracing simulations*)
> - Hard to code...?
> - After ray-tracing and BSDF calculation, annual simulation is fast
>
>
> I would not say there is a recipe. If you have to choose between 1 or 2
> CFSs, maybe it is faster to just draw them and use the 2 phase method (or
> ray-tracing if an annual simulaton is not required). On the contrary, if
> you are going to test 10 different CFSs, 3 and 5 phases may make sense,
> since you reduce the expensive ray-tracing calculations... However, this
> will also depend on weather you have the BSDF data AND/OR if it makes sense
> to calculate it and store it AND/OR if you intend to simulate a dynamically
> controlled CFS.
>
> Best!
>
> 2015-07-09 14:29 GMT-03:00 Guglielmetti, Robert <
> Robert.Guglielmetti at nrel.gov>:
>
> > Some very quick replies and clarifications within:
> >
> > On 7/9/15, 10:26 AM, "Ikrima Amaireh" <ezxia at nottingham.ac.uk> wrote:
> >
> > >Hi G. Larrain,
> > >
> > >Thanks for your detailed clarification (below).
> > >
> > >I wonder if you kindly can help me toward better understanding and
> > >answering the following:
> > >
> > >We agreed that for daylight modelling of spaces with CFS, Radiance is
> > >a suitable tool as it applies ray-tracing method. And for annual
> > >and/or climate-based daylight calculations, as calculation time
> > >becomes a critical factor, using BSDF data for CFS is highly
> > >recommended to tackle the task with radiance (using phases methods).
> However:
> >
> >
> > BSDF data in an annual simulation context is generally limited to
> > Klems basis BSDF data, which may not be high enough resolution for
> > some CFS. And the 5-phase method, which can circumvent this, is not
> necessarily "quick".
> > This is all still very much a quandary and the newest daylight metrics
> > have added confusion to all of this, IMO.
> >
> >
> > >
> > >- if someone needs to perform daylight calculations for given space
> > >with different CFS (different cases for comparison purposes) to get
> > >illumination levels for horizontal grid points (and not pictures nor
> > >scenes), is Radiance still the most convenient option?
> >
> >
> > Absolutely. The lack of an image-as-output requirement does not change
> > the fact that ray tracing is a good/convenient algorithm option for
> > daylight simulation problems, especially when dealing with diffusing
> > media and CFS in general. BSDFs allow you to do lots of "what-ifs",
> > relatively quickly, but are beholden to the limitations of the
> resolution of the BSDF.
> >
> >
> > >- is it still needed to use any of the phase methods (2, 3 or 5)?
> >
> >
> > Is what still needed? BSDF data? Ray tracing? I don't know of other
> > lighting simulation tools that can employ the multiphase methods. I
> > would say BSDF data is optional for 2-phase, required for 3-phase, and
> > optional for 5-phase.
> >
> > >- most importantly, is it still needed to get BSDF data for CFS or
> > >just can model the detailed CFS in Radiance (and, if yes, how?)
> >
> >
> > Again I'm confused as to what "it" is. A couple of approaches are
> > available to you in general. If you have a geometric model of the CFS
> > you can use Radiance (genBSDF) to make a BSDF of the CFS and use that
> > in a 3- or 5-phase context. However in an annual/climate-based
> > simulation context, you will be stuck with a Klems basis BSDF and that
> > will not be very good resolution for a lot of CFS; here you may want
> > to use the 5-phase method and stick the actual CFS geometry in the
> building model.
> >
> > Some things to consider here are the photon map, now a part of
> > Radiance proper, or using the 2-phase method where appropriate. By
> > 2-phase method I mean generating a daylight matrix for your
> > calculation points (or view), and modeling the window material as-is.
> > If the "CFS" is a shade cloth, you can approximate that with a Radiance
> "trans". Same for translucent panels.
> > With this single daylight matrix, you can throw a vector of sky
> > matrices at it and get an annual climate-based result very quickly.
> > Problem is, we want to do stuff to the windows, sometimes at the time
> step level, so:
> >
> > Blinds and compact daylight redirection devices (e.g. Lightlouver) are
> > best represented as BSDF, and if most of the redirected flux is headed
> > up and away from the points of interest, a Klems basis BSDF is good
> > enough IMO. In these cases you could use the 3-phase method. Problem
> > is when you have a BSDF for blinds, and you also want to simulate the
> > blinds-up condition (i.e. clear, specularly transmitting glass). Using
> > a Klems basis BSDF for this is sub-optimal. You end up needing to do
> > two annual simulations, one as 2-phase for the clear glass scenario,
> > and again as a 3-phase (with a blinds BSDF for the transmission
> > matrix) for the blinds down condition. If you have a lot of different
> > window groups, your simulation space can get large in a hurry. But
> > it's still do-able and you can get results that tell a story you
> > simply couldn't tell 5 years ago, informing the newest daylight metrics
> as well.
> >
> >
> >
> >
> > _______________________________________________
> > Radiance-general mailing list
> > Radiance-general at radiance-online.org
> > http://www.radiance-online.org/mailman/listinfo/radiance-general
> >
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