Illuminance falsecolor pictures

radiance-general
1

Normal 0 21 false false false DA X-NONE X-NONE MicrosoftInternetExplorer4 /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Tabel - Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-qformat:yes; mso-style-parent:""; mso-padding-alt:0cm 5.4pt 0cm 5.4pt; mso-para-margin:0cm; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan;
font-size:11.0pt; font-family:"Calibri","sans-serif"; mso-ascii-font-family:Calibri; mso-ascii-theme-font:minor-latin; mso-fareast-font-family:"Times New Roman"; mso-fareast-theme-font:minor-fareast; mso-hansi-font-family:Calibri; mso-hansi-theme-font:minor-latin; mso-bidi-font-family:"Times New Roman"; mso-bidi-theme-font:minor-bidi;} Dear Radiance users,

I have used Radiance for a couple of months mainly focusing on calculation daylightfacors. But now I want to analyze the risk for glare and visual discomfort.

I have constructed a model in Radiance in order to analyze these parameters during daytimes in an officebuilding. For this I want to use the script rpict and falsecolor.

This is how i have done build my model:

I have included the following files in my octree file: materials, constructions, windows, furniture, wheater data and surroundings.

I have used gensky to model a clear sky with sun:

Gensky 21 6 12 +s -a 51 -o -10.8 -m -15 > SkyCIESun.rad

Then I have used the following rpict and falsecolor commands:

rpict -i -vf default.vp -x 512 -y 512 kontor.oct > irrad.pic
rpict -vf default.vp -x 512 -y 512 kontor.oct > rad.pic
falsecolor -i irrad.pic -p rad.pic -cl -n 10 -l cd/m2 > lum.pic

I am not sure that these inputs are correct because I get a high contrast in the picture (black room with a white window). Therefore it is hard the separate the objects and tell the different luminances in the picture.

Does any of you have any ideas of what can be wrong and how to model luminances correctly?

Best regards

Per Haugaard

···

______________________

Per Haugaard,
Griffenfeldsgade 33, 2.tv
2200 København N
Denmark

mobil: +45 26 39 06 40
E-mail: [email protected]
       
---------------------------------

Audi, Fiat, Peugeot, Skoda, Porsche, Toyota, Ford - Kelkoo har brugte biler til en hver smag! Klik her for at sammenligne priser.

2

rpict -i -vf default.vp -x 512 -y 512 kontor.oct > irrad.pic
rpict -vf default.vp -x 512 -y 512 kontor.oct > rad.pic
falsecolor -i irrad.pic -p rad.pic -cl -n 10 -l cd/m2 > lum.pic

I am not sure that these inputs are correct because I get a high contrast in the picture (black room with a white window). Therefore it is hard the separate the objects and tell the different luminances in the picture.

Start to solve that problem step by step. It seams that the picture which you want to use as a background for the isolines is not what you expected it to be. You should have that annoying high contrast picture if you just look at rad.pic : ximage rad.pic

Usually, the output of rpict is filtered before being viewed. Read the manpage of pfilt and maybe pcond. Here you could e.g. adjust the "exposure", whih defines how the values of your rendering will be mapped to the values that your screen can actually display.

Another problem in your case might be that in your scene, the default of one ambient bounce will most probably not enough to model the reflected indirected light. Did you use a ground plan for your building (you mentioned surroundings)? You should try to render with -ab 2 or -ab 3, as light reflected from the surrounding surfaces to the ceiling and walls, and from there to floor, ceiling, walls, may have a big influence of the result.

Forget about falsecolor until you got the previous steps in the process running. First you need the background image, before you solved that you do not need to worry how to combine it with contour lines. BUT also for irrad.pic, you should definitely increase the ambient parameters for the scene as you described it.

Good luck, Lars.

3

There are a few things you can do to improve the falsecolor output. The
accurate output from rpict is another topic, but it seems that you're
mainly interested in displaying your data.

> falsecolor -i irrad.pic -p rad.pic -cl -n 10 -l cd/m2 > lum.pic

Your command was missing at least one important item, a maximum for the
scale. If your maximum illuminance in the scene that you're interested
in is say 2000 lux you should add that to your falsecolor command.

Also if you are using the numerical data from the irrad.pic, the label
should be for illuminance, lux, unless you are converting to something
else.

falsecolor -i irrad.pic -p rad.pic -cl -n 10 -l lux -s 2000 > illum.pic

A few more items that you can add to make it more legible... Try a
greater number of steps to your scale, maybe up to 20, although this
might be too many for a 512 pixel image. If your image was larger you
could make your scale larger with the -lh and -lw options. Also if you
have a high range and want to see detail at the low end of the scale
while still registering values at the high end you could try a
logarithmic scale, I think a base around the natural log 2.718 usually
shows the range well.

falsecolor -i irrad.pic -p rad.pic -cl -n 20 -l lux -s 2000 -log 2.718 >
illum.pic

Try a few variations of the scale, log base, and number of divisions
until you get something legible.

-Chris

···

____________________________________________________________
Electronic mail messages entering and leaving Arup business
systems are scanned for acceptability of content and viruses

4

Christopher Rush wrote:

Your command was missing at least one important item, a maximum for the scale. If your maximum illuminance in the scene that you're interested in is say 2000 lux you should add that to your falsecolor command.

An easy way to get the maximum value in the image is to use pextrem, like so: pextrem -o lum.pic

pextrem will print two sets of rgb values to the standard output, the max and the min pixel values in the image.

The main problem I see though, is--if I'm inferring the correct usage from the image filenames--is you're using an illuminance pic as the input to falsecolor but you're expecting to see nits? And you mention that you're interested in computing DFs? It seems as though you're mixing and matching your units here. It is important to remember that falsecolor has no idea what the images represent, you have to supply that info and there is no error checking. So you could easily supply falsecolor with an illuminance pic and place a cd/m^2 label, as it appears you have done and Chris has pointed out as a problem...

A few more items that you can add to make it more legible... Try a greater number of steps to your scale, maybe up to 20, although this might be too many for a 512 pixel image. If your image was larger you could make your scale larger with the -lh and -lw options. Also if you have a high range and want to see detail at the low end of the scale while still registering values at the high end you could try a logarithmic scale, I think a base around the natural log 2.718 usually shows the range well.

This is great advice. These images are quite powerful ways to convey a lot of scene information in one view, but the onus is on the user to make sure the image tells a fair story. This means dialing in the scale logarithmically to present a fair case for contrast, setting the scale maximum to fairly include the extrema (or at least identifying the extrema with the -e option to falsecolor) and of course making sure you're presenting the correct units.

- Rob

5

As Lars already pointed out you have to increase the rendering parameters. The default for
rpict is to render 0 ambient bounces (reflections). Without an explicit '-ab' you will only see
the sky through the window but nothing that is illuminated by it. That's why you get a black
and white picture. Try something like '-ab 2' for a test rendering and then increase it to 4 or
5 for the final rendering.

You only need a high value of '-ab' for the irridiance picture. The second picture is only
used as a backdrop to the contour lines and doesn't have to be accurate. Consider also
the use of an ambient cache file ('-af') to reuse the ambient information calculated in the first
rpict call. This will speed up the rendering of the second picture, even with high ambient
settings.

Once your pictures render to your satisfaction you will have to play around with the
scale of your contour lines. From your description I understand that your scene contains
both window and room. In this situation you will most likely see no lines on the window/sky
(scale too small but correct for the room interior) or no lines on the room surfaces (scale
too large for room). A logarithmic scale might help here but the people who are looking
at these pictures have to know what it means.

Regards,
Thomas

···

On 23 Apr 2008, at 14:33, Per Haugaard wrote:

Then I have used the following rpict and falsecolor commands:

rpict -i -vf default.vp -x 512 -y 512 kontor.oct > irrad.pic
rpict -vf default.vp -x 512 -y 512 kontor.oct > rad.pic
falsecolor -i irrad.pic -p rad.pic -cl -n 10 -l cd/m2 > lum.pic

I am not sure that these inputs are correct because I get a high contrast in the picture (black room with a white window).