[Radiance-general] Understanding rtcontrib - trouble with tregenza skypatches

[Greg Ward]

Yes, you've no doubt identified one of the main difficulties in understanding a functional language.  Everything is defined in terms of everything else, and there's no explicit "flow" to a program, which is really just a set of equations.  Only when something is evaluated does anything happen, then whatever variables and functions that evaluation requires causes a cascade that leads to inputs that are somehow predefined in the environment.

In the case of .cal files used in a Radiance rendering, most of these variables and functions are given or described in rayinit.cal.  Similarly, the direction vector (Dx,Dy,Dz) and world position (Px,Py,Pz) variables are the ones used primarily by .cal files given on the rcontrib command line.  You will see these mentioned in the comments and main section of tregenza.cal.

The best introduction to .cal files is probably still Chapter 4 of "Rendering with Radiance," which you can order from Randolph Fritz if you don't already have a copy.

Best,
-Greg

> From: "Secure-Mail User" <harrym at secure-mail.biz>
> Date: August 26, 2013 5:46:06 PM PDT
> 
> Hi Greg,
> 
> This works perfectly :) Thanks a lot.
> 
> Functions in Radiance are something that I tend to have trouble with. When looking at the .cal files, I often find it difficult to understand where inputs and outputs are defined. Would anyone know a good resource I could look into that could help? Is it a linux thing? To give you a hint of where I'm coming from: I have some reasonable understanding of languages like Python, Ruby and a little C# but am fairly illiterate when it comes to Linux. 
> 
> Cheers
> 
> 
> --- Ursprüngliche Nachricht ---
> Von: Greg Ward <gregoryjward at gmail.com>
> Datum: 26.08.2013 18:07:27
> An: harrym at secure-mail.biz, Radiance general discussion <radiance-general at radiance-online.org>
> Betreff: Re: [Radiance-general] Understanding rtcontrib - trouble with tregenza skypatches
> 
> You need to *add* -bn Ntbins after your -f tregenza.cal argument.  Don't remove the -b option -- you need that as well.
> 
> The original rtcontrib didn't absolutely require -bn, although it should have.  The new rcontrib (which "rtcontrib" points to) does.
> 
> Best,
> -Greg
> 
>> From: "Secure-Mail User" <harrym at secure-mail.biz>
>> Date: August 26, 2013 3:08:47 AM PDT
>> 
>> Hi All,
>>  
>> I’m going through the “Understanding rtcontrib” tutorial and got stuck when trying to get the Tregenza sky patches to work (page 16). I can't figure out how to use the tregenza function and the binning with rcontrib:
>>  
>> DIMS=600
>> vw="-x $DIMS -y $DIMS -vf views/sky.vf"
>> oconv materials/testroom.mat objects/testroom.rad skies/sky_white.rad > testroom_whitesky.oct
>> vwrays -ff $vw |rcontrib @rtc.opt -ffc $(vwrays -d $vw) –V+ -f tregenza.cal -b tbin -o images/patches/p%03d.hdr -m sky_glow testroom_whitesky.oct
>>  
>> Which returns:
>>  
>> rcontrib: fatal - unspecified or illegal bin count for modifier 'sky_glow'
>>  
>> My setup:
>> Windows 7
>> Cygwin
>> NREL’s latest Radiance version
>>  
>>  
>> What I tried so far:
>>  
>> -          Googling the error took me to the rcontrib.c source code... interesting but not immediately helpful
>> -          Changing when –f ..... –b ... is specified which didn’t change the output (which is also stated in rtcontrib man page as I found out later)
>> -          I checked sky_white.rad and compared it with what is shown in the tutorial. Tick.
>> -          I checked my spelling multiple times..... (hopefully) Tick
>> -          Replacing “-b tbin” with “-bn 146”, accidently with the view file back.vf, which resulted in a single, fairly dark picture. When repeating the command to look at the sky hemisphere, I get a uniform sky at around 178 cd/m²
>>  
>> Could anybody point me to my mistake?
>>  
>> Many Thanks in advance,
>> HM
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