[Radiance-general] genskyvec with HDR sky view?

[Andy McNeil]

>
> You haven’t ever used a HDR sky with rcontrib, by the way?

Yes, I have. I'm working for Terrestrial Light: http://terrestriallight.com/
which makes HDR cameras for building control systems.

On Wed, Jun 1, 2016 at 8:48 AM, Achim Geissler <achim.geissler at intergga.ch>
wrote:

> Hi Andy,
>
>
>
> that worked like a charm, thanks! The .cal file I was using originated
> from a source using “specific” fisheye lenses … hmm. More work to do.
>
>
>
> You haven’t ever used a HDR sky with rcontrib, by the way?
>
>
>
> Best
>
> Achim
>
>
>
>
>
>
>
> *Von:* Andy McNeil [mailto:mcneil.andrew at gmail.com]
> *Gesendet:* Mittwoch, 1. Juni 2016 17:00
>
> *An:* Radiance general discussion
> *Betreff:* Re: [Radiance-general] genskyvec with HDR sky view?
>
>
>
> @Andy: Incidentally, this is in regard to one step before tackling
> genskyvec
> again, I am trying to generate a view of a scene via "sky_glow source sky"
> based on the HDR ... the scene has a ground plane, but does have a "hole"
> between this and the sky (which works with "normal" skies). I'll try your
> suggestion for the sky definition, thanks!
>
>
>
> Oh, I didn't realize it was a cal file issue. Have you considered using
> fisheye.cal? It is distributed with the radiance auxiliary files (get them
> here:
> http://radiance-online.org/download-install/radiance-source-code/un-official-head-version
> look in here: ray/lib/fisheye.cal). Here's how I use it, which I found
> somewhere else along the way:
>
>
>
> void colorpict skypict
>
> 11 red green blue sky_image.hdr fisheye.cal fish_u fish_v -rx 90 -rz 180
>
> 0
>
> 0
>
>
>
> skypict glow skyglow
>
> 0
>
> 0
>
> 4 1 1 1 0
>
>
>
> skyglow source sky
>
> 0
>
> 0
>
> 4 0 0 1 180
>
>
>
> Andy
>
>
>
>
>
> On Wed, Jun 1, 2016 at 1:08 AM, Achim Geissler <achim.geissler at intergga.ch>
> wrote:
>
> Hi Greg,
>
> sorry to be somehow seemingly rubbing you the wrong way - I can't remember
> you ever telling anybody else simply to "give up" :o( . It is definitely
> not
> intentional (and I may note here that I am not a native English
> speaker/writer).
>
> The formatting was O.K. with html mail format. Whatever.
>
> The Photosphere stuff was simply to try to give some information on the HDR
> in respond to your statements in regard to same (kind of "prove" that it is
> actually a Radiance readable HDR ...).
>
> The comments on orienting the HDR are noted. I accept that if I do it
> right,
> it should be correct  ;o)
>
> I wasn't planning to rewrite genskyvec.pl, but you have me confused on
> how I
> should "prepare a sky file it will accept" - which is clearly my goal -
> without understanding at least partially how it works / what the data flow
> is / what it needs.
>
> Actually, the number of the warnings increased significantly and no result
> was obtained. With skyfunc_hdr a (not very useful) result was generated
> with
> "some" identical warning messages.
>
> @Andy: Incidentally, this is in regard to one step before tackling
> genskyvec
> again, I am trying to generate a view of a scene via "sky_glow source sky"
> based on the HDR ... the scene has a ground plane, but does have a "hole"
> between this and the sky (which works with "normal" skies). I'll try your
> suggestion for the sky definition, thanks!
>
> Skymap.cal is
> ===
> u = 1 - (0.5 + DDx *r);
> v = 0.5 + DDy *r;
>
> r = if(DD, 0.707106781*(sin(acos(DDz)/2))/DD,0);
>
> DD = sqrt(DDx*DDx + DDy*DDy);
>
> DDy = Py*norm;
> DDx = Px*norm;
> DDz = Pz*norm;
>
> norm = 1/sqrt(Py*Py + Px*Px + Pz*Pz);
> ===
>
> I'll go back to RWR again and see what I can learn.
>
> Thanks.
>
> Best
> Achim
>
>
> -----Ursprüngliche Nachricht-----
> Von: Greg Ward [mailto:gregoryjward at gmail.com]
> Gesendet: Mittwoch, 1. Juni 2016 00:18
>
> An: Radiance general discussion
> Betreff: Re: [Radiance-general] genskyvec with HDR sky view?
>
> Hi Achim,
>
> I'll answer inline again, making a bad formatting job look even worse....
>
> > From: "Achim Geissler" <achim.geissler at intergga.ch>
> > Date: May 30, 2016 8:05:25 AM PDT
> >
> > Hi Greg,
> >
> > thanks for the pointers. I am afraid, though, that I was unable to
> > really make heads or tails of them.
> > a) HDR file (Photosphere)
> >       i, the (test) HDR gives min/max values in falsecolor view of 39 to
> > 2900, whatever the unit, there
> >       ii, it gives histogram min/max values  for Luminance of 34.8 to
> > 4.43E+06
> >       iii, it does not seem to be clipped
>
> I don't know what (i), (ii) and (iii) refer to, if anything.  Are these
> particular processes you have tried?  If so, what are they?
>
> Typically, falsecolor and Photosphere report photometric values (i.e.,
> radiance values times 179 lumens/watt efficacy).
>
> > b) There is a sun (albeit behind a thin cloud cover). Simply adding a
> > sun definition to my sky description did not really change anything,
> though.
> > Also, at this point I do not know which r,g,b radiance values to use
> > for the solar "light" material and do these influence the result? And,
> > actually, how to exactly position the HDR so that the sun positions
> tally.
>
> If you have your sky turned the right way around, so that the Z-axis points
> up, Y-axis points north, and X-axis points east, then positioning the sun
> is
> a matter of running gensky with the appropriate date/time and global
> position parameters, and extracting the description it generates.  You can
> adjust the solar radiance values to match the global-diffuse measured that
> day using the -R option to gensky.
>
> > c) I took a look at the genskyvec.pl script, however, I am not
> > perl-literate so that is a bit difficult. I seem to be missing out on
> > where this script >could< use values from the HDR file to generate the
> > sky vectors. Part of the code seems to be a copy of the setting up of
> patches from reinhart.cal.
> > Also, the "skyfunc glow skyglow" and "skyglow source sky" are written
> > to the
> > (an) octree in the script. Can I ignore that? Or does that let me
> > leave these definitions out of my sky description? Which definition has
> precedent?
> > I can't really see where the "skybright.cal" values from a standard
> > gensky sky would come into play - this should be what is replaced by
> > values from the HDR?
>
> I'm not suggesting you rewrite genskyvec.  Rather, I'm suggesting that you
> prepare a sky file it will accept and run it on that file.  If this doesn't
> make sense, then I suggest you give up.
>
> > d) using the sky description as below but with "skyfunc" gives
> > rpict: warning - compute error for colorpict "skyfunc"
> > rpict: Division by zero
> > when trying to generate a view of a scene.
>
> I don't know why globally replacing "skyfunc_hdr" with "skyfunc" in your
> file should cause new errors.  You must have done something else, or the
> original run would have generated the same errors.  I don't know what's in
> "map_sky.cal", which is the likely cause.
>
> > I must admit the flow of data (input / output) in all the definitions
> > is a bit of a mystery, for me. I did find a kind of description for
> > colorpict in p_data.c, but that didn't really help, sadly. Looking at
> > your code, I get the feeling I am not literate in any programming
> > language ... :o(
>
> Well, it's not particularly transparent, I will grant you.  There's this
> back-and-forth between the ray tracing and the scene description, such that
> when a material is intersected, it queries its modifiers, which calls back
> to your map_sky.cal file in a rather convoluted fashion.
>
> You should look through Chapter 4 of "Rendering with Radiance."  Starting
> at
> Section 4.1.4, we talk about how the interaction between rendering and .cal
> files operates.
>
> > If you (or, of course, anyone else out there that has done this
> > before) can give any further help or tips, it would be much appreciated.
> >
> > Best
> > Achim
> >
> >
> > -----Ursprüngliche Nachricht-----
> > Von: Greg Ward [mailto:gregoryjward at gmail.com]
> > Gesendet: Samstag, 28. Mai 2016 01:27
> > An: Radiance general discussion
> > Betreff: Re: [Radiance-general] genskyvec with HDR sky view?
> >
> > Hi Achim,
> >
> > I wouldn't call what you are trying to do "easy," even if others have
> > done it.  Your HDR file has to be in the correct units or scaled by
> > the right amount to get calibrated radiance values, and even then, the
> > sun is usually out of range(clipped) and won't be properly sampled if it
> is a clear sky.
> >
> > As you noted, such a sky cannot be given as input to genskyvec, which
> > expects a very specific set of primitives output by gensky or gendaylit.
> > Specifically, you need to name your colorpict pattern "skyfunc" and
> > add a solar source if the sky is sunny.  You could try to modify your
> > description to match, but you'd have to look at the Perl script
> > src/util/genskyvec.pl to figure out how to satisfy the input
> requirements.
> >
> > Once you have a sky description, you can use rtrace with the -I option
> > to compute hemispherical irradiance, from which you can create an
> > adjustment factor to apply to your glow based on horizontal irradiance.
> >
> > It's all possible, but the details are not very straightforward.
> >
> > Best,
> > -Greg
> >
> >> From: Achim Geissler <achim.geissler at intergga.ch>
> >> Date: May 27, 2016 12:29:35 PM PDT
> >>
> >> Hi all,
> >>
> >> after searching high and low without clear results apart from a lot
> >> of
> > pointers that “everybody seems to be doing it” (so it should actually
> > be easy and I am probably missing the forest due to seeing trees, as
> > they say) a short question: The goal is to use HDR (fisheye) views of
> > the sky for radiance calculations. All I could manage to date are
> > pretty pictures with HDR skies. Ideally, the workflow would be “the
> > same” as when using a sky from gensky or gendaylit. E.g., it would be
> > nice to be able to generate the sky vectors (genskyvec) from the HDR
> > sky view. Is that possible? How? Trying to simply pipe a sky
> > definition along the lines of
> >>
> >> void colorpict skyfunc_hdr
> >> 7 red green blue sky_image.hdr map_sky.cal u v
> >> 0
> >> 0
> >>
> >> skyfunc_hdr glow sky_glow_hdr
> >> 0
> >> 0
> >> 4 1 1 1 0
> >>
> >> sky_glow_hdr source sky_hdr
> >> 0
> >> 0
> >> 4 0 0 1 180
> >>
> >> into genskyvec didn’t work - well, would have been too simple (the
> > map_sky.cal is from the PhD by Coralie Cauwerts, 2013). The following
> > approaches resulted in the “pretty pictures” (replacing “source”
> > above)
> >>
> >> sky_glow_hdr bubble sky_hdr
> >> 0
> >> 0
> >> 4 0 0 0 2000
> >>
> >> or
> >>
> >> !genbox sky_glow_hdr boxenv 2000 2000 1000 -i | xform -t -1000 -1000
> >> -500
> >>
> >> A further topic will be a “calibration” of the HDR sky views - we
> >> have
> > global horizontal and diffuse horizontal radiation values available.
> > The current idea of a (possibly slightly rough) method of calibration
> > would be to use the HDR sky to calculate the corresponding sensor
> > value with radiance and “somehow” introduce a scaling factor into the
> > HDR sky such that the measured and calculated global horizontal radiation
> values tally.
> >>
> >> Thanks for any hints & ideas!
> >>
> >> Best
> >> Achim
> >>
> >> achim.geissler at intergga.ch
>
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