[Radiance-general] mkillum usage

[Marija Velickovic]

Hi,

I've been thinking about mkllum usage and parameters for mkillum
calculation. I've explored mailing list and my private archives and also
RWR book, and come to some conclusions, but also some questions.


All notes below are for few types of daylight simulations, where windows
with/without fenestration are (not)treated with mkillum.

########

*Luminance images calculation*
Based on RWR page 351
“For image generation, the conversion of a window to a light source using
the mkillum utility can significantly speed up the production of smooth
renderings. The technique works well as long as the total number of
secondary light sources is kept reasonably small.”

“For those rare occasions when images need to be rendered using high value
for -ab, it may be best to avoid using secondary sources and rely on
ambient calculation.”

Classical usage of these ideas is usage of mkillum either manually or
through rad program, for window surfaces.
Mkillum parameters:

   - -ab 2 is usually sufficient if building exterior is not too complex.
   If illum surfaces should seal some complex shading system (Venetian blinds)
   this parameter should be >2.
   - other parameters - default values can be used because they are
   sufficiently high
   - -aa 0 can be used when mkillum is used for Venetian blinds output
   calculation
   - -av r g b is set to:
      - if glazing is between building exterior and interior -  av should
      be set to *“ground ambient value*” obtained from gensky command.
      - if glazing is between exterior and interior for upper floors in the
      building - use the same value as for bottom floors
      - if glazing is between two interior areas - either use 0 0 0 (which
      will always underestimate values) or use the compamb script with interior
      views to come up with a good setting

*Question:* If outside environment is heavily obstructed, as it is usually
the case in urban areas, how should we determine -av value for mkillum
calculation? I think that simple usage of 'ground ambient value' for -av
would overestimate luminance inside of the building.
Rad parameters:
Beside setting of ambient parameters it is good idea to experiment a little
and find nice set of -d* parameters.
Example of parameters: -ab 3 -av 0 0 0 -ad 1024 -as 256 -aa 0.1 -ar 600 -ps
1 -ds 0.05 -dj 1 -dt 0.03 -dc 0.9 -af tmp/floor1_illum.amb

###
*Illuminance images calculation*
Based on RWR page 351:
“For illuminance calculations, where -ab >2 is usually essential, the
preprocessing of windows to secondary light sources is generally not
recommended.”

Illuminance calculations are needed for DF or Autonomy calculations.

*DF calculations*
Generally this approach is used in dayfact script, where illuminance on a
workplane is calculated with rtrace -I option, and rather high parameters
are recommended eg: -ab 5 -av 0 0 0 -ad 2048 -as 512 -aa 0.1 -ar 600 -af
tmp/amb_file.amb

*Question:* Why it is not recommended to use mkillum for illuminance
calculations?
I've tried to include mkillum for DF calculation on workplane, and set
parameters with similar manner like for luminance images - and internal
illuminances were much higher then without mkillum (with same rtrace
parameters for the image).

So I need some answer if for illuminace calc approach with mkillum gives
wrong results, or parameters should be set differently.

*Autonomy calculations*
These are also illuminace calculations, but since numerous time moments are
included, mkillum doesn't have any sense to be used.
For this we can use 3-phase method, or Daysim approach - and calculate with
high ambient parameters.

###

So if we say it all in short: what is bothering me the most is -av setting
for mkillum, because "ground ambient values" seem to high for real project
cases where there is complex environement outside of the building.

Any info about list members' experience with mkillum and daylighting is
welcome.

Thanks in advance,
Marija
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