[Radiance-general] Could RTRACE produce two outputs (picture and values)?

[Lars O. Grobe]

Hi Mirjam,

pixel values in a hdr file are nothing but binary-coded triplets of 
irradiance data in three channels (RGB) if you render your irradiance 
hdr image. If you have an image file containing these illuminance 
values, you can extract the data to e.g. ASCII columns using pvalue -o 
Outcome.hdr. pvalue does not interpret the data and thus does not care 
about it being irradiance or radiance, it just converts between codings. 
The -o makes sure to use the original pixel values in case any exposure 
correction had been appiled (uncommon with irradiance maps).

The advantage in using a sensor grid, not an image, to calculate 
illuminance is that you would typically use a rather coarse grid, with 
less sensor locations to be calculated. This saves time per sensor, 
allowing higher accuracy at each location. So you may prefer very high 
ambient settings for a 10 x 10 sensor grid over a 1024x1024 pixel image, 
which may force you to reduce the accuracy. This assumes that you do not 
loose relevant information from the reduced resolution (e.g. a sensor 
may happen to be shadowed by a thin frame, which would lead to 
underestimates if interpolation between sensor values is applied).

You can also use pvalue -r to create a hdr image from your ASCII columns 
of irradiance / radiance values. In that case, some information on the 
x/y dimensions must be given.

Of course, recoding pixel values does not allow you to translate 
irradiance into radiance or vice versa...

Cheers, Lars.
> Dear all,
>
> Just a short question, unfortunately I wasn't able to find the answer 
> on the Radiance-community:
>
> *Is it possible to create two outputs using RTRACE: *
>
> -a .hdr picture and
>
> -a text file containing illuminance values.
>
> In case of a virtual plane, rtrace has to be used instead of rpict (as 
> explained in the Radiance Tutorial). Now, I'm doing the same 
> simulation twice in order to get 2 outputs which takes a lot of time. 
> Isn't it possible to create 2 outputs through only 1 simulation?
>
> If not, could pvalue help me on this one? And if yes, how? Or would 
> pvalue only would give me luminance values?
>
> First simulation:
>
> echo "     Rtrace illuminance "
>
> vwrays -x $Dims -y $Dims -vf viewfile.vf \
>
> | rcalc -e '$1=$1; $2=$2; $3=0.75; $4=$4; $5=$5; $6=1' \
>
> | rtrace -w -ab 3 -fac -I -ov `vwrays -d -vf viewfile.vf -x $Dims -y 
> $Dims` scene.oct >  Outcome.hdr
>
> Second simulation:
>
> echo "     Rtrace illuminance values "
>
> vwrays -x $Dimstable -y $Dimstable -vf viewfile.vf \
>
> | rcalc -e '$1=$1; $2=$2; $3=$3; $4=$4; $5=$5; $6=1' \
>
> | rtrace -w -I -h -ov -ab 2 `vwrays -d -vf viewfile.vf -x $Dims -y 
> $Dims` scene.oct | rcalc -e '$1=$1*179' > Outcome.txt
>
> Thanks in advance for your help!
>
> Best regards,
>
> Mirjam
>

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